function Tiled (id) {
  var obj = document.getElementById(id);
  var self = this;
  this.modal = null;
  this.curframe = undefined;

Close

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

  this.tile = function () {

Close

enforce a maximum number of statements allowed in function blocks (max-statements)

The max-statements rule allows you to specify the maximum number of statements allowed in a function.

function foo() {
  var bar = 1; // one statement
  var baz = 2; // two statements
  var qux = 3; // three statements
}

Rule Details

This rule enforces a maximum number of statements allowed in function blocks.

Options

This rule has a number or object option:

• "max" (default 10) enforces a maximum number of statements allows in function blocks

Deprecated: The object property maximum is deprecated; please use the object property max instead.

This rule has an object option:

• "ignoreTopLevelFunctions": true ignores top-level functions

max

Examples of incorrect code for this rule with the default { "max": 10 } option:

/*eslint max-statements: ["error", 10]*/
/*eslint-env es6*/

function foo() {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;

  var foo11 = 11; // Too many.
}

let foo = () => {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;

  var foo11 = 11; // Too many.
};

Examples of correct code for this rule with the default { "max": 10 } option:

/*eslint max-statements: ["error", 10]*/
/*eslint-env es6*/

function foo() {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;
  return function () {

    // The number of statements in the inner function does not count toward the
    // statement maximum.

    return 42;
  };
}

let foo = () => {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;
  return function () {

    // The number of statements in the inner function does not count toward the
    // statement maximum.

    return 42;
  };
}

ignoreTopLevelFunctions

Examples of additional correct code for this rule with the { "max": 10 }, { "ignoreTopLevelFunctions": true } options:

/*eslint max-statements: ["error", 10, { "ignoreTopLevelFunctions": true }]*/

function foo() {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;
  var foo11 = 11;
}

Related Rules

• [complexity](complexity.md)
• [max-depth](max-depth.md)
• [max-len](max-len.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md) Source: http://eslint.org/docs/rules/

  this.other_frame = function (dir) {

Close

Limit Cyclomatic Complexity (complexity)

Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.

function a(x) {
    if (true) {
        return x; // 1st path
    } else if (false) {
        return x+1; // 2nd path
    } else {
        return 4; // 3rd path
    }
}

Rule Details

This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20).

Examples of incorrect code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else if (false) {
        return x+1;
    } else {
        return 4; // 3rd path
    }
}

Examples of correct code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else {
        return 4;
    }
}

Options

Optionally, you may specify a max object property:

"complexity": ["error", 2]

is equivalent to

"complexity": ["error", { "max": 2 }]

Deprecated: the object property maximum is deprecated. Please use the property max instead.

When Not To Use It

If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.

Further Reading

• About Complexity
• Complexity Analysis of JavaScript Code

Related Rules

• [max-depth](max-depth.md)
• [max-len](max-len.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

  this.new_frame = function (name, body, update, pos, cb) {

Close

enforce a maximum number of statements allowed in function blocks (max-statements)

The max-statements rule allows you to specify the maximum number of statements allowed in a function.

function foo() {
  var bar = 1; // one statement
  var baz = 2; // two statements
  var qux = 3; // three statements
}

Rule Details

This rule enforces a maximum number of statements allowed in function blocks.

Options

This rule has a number or object option:

• "max" (default 10) enforces a maximum number of statements allows in function blocks

Deprecated: The object property maximum is deprecated; please use the object property max instead.

This rule has an object option:

• "ignoreTopLevelFunctions": true ignores top-level functions

max

Examples of incorrect code for this rule with the default { "max": 10 } option:

/*eslint max-statements: ["error", 10]*/
/*eslint-env es6*/

function foo() {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;

  var foo11 = 11; // Too many.
}

let foo = () => {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;

  var foo11 = 11; // Too many.
};

Examples of correct code for this rule with the default { "max": 10 } option:

/*eslint max-statements: ["error", 10]*/
/*eslint-env es6*/

function foo() {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;
  return function () {

    // The number of statements in the inner function does not count toward the
    // statement maximum.

    return 42;
  };
}

let foo = () => {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;
  return function () {

    // The number of statements in the inner function does not count toward the
    // statement maximum.

    return 42;
  };
}

ignoreTopLevelFunctions

Examples of additional correct code for this rule with the { "max": 10 }, { "ignoreTopLevelFunctions": true } options:

/*eslint max-statements: ["error", 10, { "ignoreTopLevelFunctions": true }]*/

function foo() {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;
  var foo11 = 11;
}

Related Rules

• [complexity](complexity.md)
• [max-depth](max-depth.md)
• [max-len](max-len.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md) Source: http://eslint.org/docs/rules/

  this.del_frame = function (name) {

Close

Limit Cyclomatic Complexity (complexity)

Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.

function a(x) {
    if (true) {
        return x; // 1st path
    } else if (false) {
        return x+1; // 2nd path
    } else {
        return 4; // 3rd path
    }
}

Rule Details

This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20).

Examples of incorrect code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else if (false) {
        return x+1;
    } else {
        return 4; // 3rd path
    }
}

Examples of correct code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else {
        return 4;
    }
}

Options

Optionally, you may specify a max object property:

"complexity": ["error", 2]

is equivalent to

"complexity": ["error", { "max": 2 }]

Deprecated: the object property maximum is deprecated. Please use the property max instead.

When Not To Use It

If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.

Further Reading

• About Complexity
• Complexity Analysis of JavaScript Code

Related Rules

• [max-depth](max-depth.md)
• [max-len](max-len.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

  this.tile = function () {

Close

Limit Cyclomatic Complexity (complexity)

Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.

function a(x) {
    if (true) {
        return x; // 1st path
    } else if (false) {
        return x+1; // 2nd path
    } else {
        return 4; // 3rd path
    }
}

Rule Details

This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20).

Examples of incorrect code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else if (false) {
        return x+1;
    } else {
        return 4; // 3rd path
    }
}

Examples of correct code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else {
        return 4;
    }
}

Options

Optionally, you may specify a max object property:

"complexity": ["error", 2]

is equivalent to

"complexity": ["error", { "max": 2 }]

Deprecated: the object property maximum is deprecated. Please use the property max instead.

When Not To Use It

If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.

Further Reading

• About Complexity
• Complexity Analysis of JavaScript Code

Related Rules

• [max-depth](max-depth.md)
• [max-len](max-len.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

  this.move_frame = function (dir) {

Close

Limit Cyclomatic Complexity (complexity)

Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.

function a(x) {
    if (true) {
        return x; // 1st path
    } else if (false) {
        return x+1; // 2nd path
    } else {
        return 4; // 3rd path
    }
}

Rule Details

This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20).

Examples of incorrect code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else if (false) {
        return x+1;
    } else {
        return 4; // 3rd path
    }
}

Examples of correct code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else {
        return 4;
    }
}

Options

Optionally, you may specify a max object property:

"complexity": ["error", 2]

is equivalent to

"complexity": ["error", { "max": 2 }]

Deprecated: the object property maximum is deprecated. Please use the property max instead.

When Not To Use It

If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.

Further Reading

• About Complexity
• Complexity Analysis of JavaScript Code

Related Rules

• [max-depth](max-depth.md)
• [max-len](max-len.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

  this.del_frame = function (name) {

Close

enforce a maximum number of statements allowed in function blocks (max-statements)

The max-statements rule allows you to specify the maximum number of statements allowed in a function.

function foo() {
  var bar = 1; // one statement
  var baz = 2; // two statements
  var qux = 3; // three statements
}

Rule Details

This rule enforces a maximum number of statements allowed in function blocks.

Options

This rule has a number or object option:

• "max" (default 10) enforces a maximum number of statements allows in function blocks

Deprecated: The object property maximum is deprecated; please use the object property max instead.

This rule has an object option:

• "ignoreTopLevelFunctions": true ignores top-level functions

max

Examples of incorrect code for this rule with the default { "max": 10 } option:

/*eslint max-statements: ["error", 10]*/
/*eslint-env es6*/

function foo() {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;

  var foo11 = 11; // Too many.
}

let foo = () => {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;

  var foo11 = 11; // Too many.
};

Examples of correct code for this rule with the default { "max": 10 } option:

/*eslint max-statements: ["error", 10]*/
/*eslint-env es6*/

function foo() {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;
  return function () {

    // The number of statements in the inner function does not count toward the
    // statement maximum.

    return 42;
  };
}

let foo = () => {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;
  return function () {

    // The number of statements in the inner function does not count toward the
    // statement maximum.

    return 42;
  };
}

ignoreTopLevelFunctions

Examples of additional correct code for this rule with the { "max": 10 }, { "ignoreTopLevelFunctions": true } options:

/*eslint max-statements: ["error", 10, { "ignoreTopLevelFunctions": true }]*/

function foo() {
  var foo1 = 1;
  var foo2 = 2;
  var foo3 = 3;
  var foo4 = 4;
  var foo5 = 5;
  var foo6 = 6;
  var foo7 = 7;
  var foo8 = 8;
  var foo9 = 9;
  var foo10 = 10;
  var foo11 = 11;
}

Related Rules

• [complexity](complexity.md)
• [max-depth](max-depth.md)
• [max-len](max-len.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md) Source: http://eslint.org/docs/rules/

  this.new_frame = function (name, body, update, pos, cb) {

Close

Limit Cyclomatic Complexity (complexity)

Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.

function a(x) {
    if (true) {
        return x; // 1st path
    } else if (false) {
        return x+1; // 2nd path
    } else {
        return 4; // 3rd path
    }
}

Rule Details

This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20).

Examples of incorrect code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else if (false) {
        return x+1;
    } else {
        return 4; // 3rd path
    }
}

Examples of correct code for a maximum of 2:

/*eslint complexity: ["error", 2]*/

function a(x) {
    if (true) {
        return x;
    } else {
        return 4;
    }
}

Options

Optionally, you may specify a max object property:

"complexity": ["error", 2]

is equivalent to

"complexity": ["error", { "max": 2 }]

Deprecated: the object property maximum is deprecated. Please use the property max instead.

When Not To Use It

If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.

Further Reading

• About Complexity
• Complexity Analysis of JavaScript Code

Related Rules

• [max-depth](max-depth.md)
• [max-len](max-len.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

      for (var k in Object.keys(style)) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

      var width = w;

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

      var height = h - mtop;

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

      for (var row in this.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

      for (var row in this.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

      for (var row in this.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

      var mtop = topmargin;

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

    var left = 0;

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

        cb(self, nf);

Close

Enforce Return After Callback (callback-return)

The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.

function doSomething(err, callback) {
    if (err) {
        return callback(err);
    }
    callback();
}

To prevent calling the callback multiple times it is important to return anytime the callback is triggered outside of the main function body. Neglecting this technique often leads to issues where you do something more than once. For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw a Can't render headers after they are sent to the client. error.

Rule Details

This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately preceding a return statement. This rule decides what is a callback based on the name of the function being called.

Options

The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback, cb, next.

Default callback names

Examples of incorrect code for this rule with the default ["callback", "cb", "next"] option:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        callback(err);
    }
    callback();
}

Examples of correct code for this rule with the default ["callback", "cb", "next"] option:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        return callback(err);
    }
    callback();
}

Supplied callback names

Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]:

/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/

function foo(err, done) {
    if (err) {
        done(err);
    }
    done();
}

function bar(err, send) {
    if (err) {
        send.error(err);
    }
    send.success();
}

Examples of correct code for this rule with the option ["done", "send.error", "send.success"]:

/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/

function foo(err, done) {
    if (err) {
        return done(err);
    }
    done();
}

function bar(err, send) {
    if (err) {
        return send.error(err);
    }
    send.success();
}

Known Limitations

Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:

• false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
• false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)

Passing the callback by reference

The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout).

Example of a false negative when this rule reports correct code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        setTimeout(callback, 0); // this is bad, but WILL NOT warn
    }
    callback();
}

Triggering the callback within a nested function

The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).

Example of a false negative when this rule reports correct code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        process.nextTick(function() {
            return callback(); // this is bad, but WILL NOT warn
        });
    }
    callback();
}

If/else statements

The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if statement.

Example of a false positive when this rule reports incorrect code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        callback(err); // this is fine, but WILL warn
    } else {
        callback();    // this is fine, but WILL warn
    }
}

When Not To Use It

There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.

Further Reading

• The Art Of Node: Callbacks
• Nodejitsu: What are the error conventions?

Related Rules

• [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/

              for (var row in this.frames[col]) {

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

      var f = this.curframe[0];

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

      var cols = this.frames.length;

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

              for (var row in this.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

      var left = 0;

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

        for (var row in self.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

          cb(self, nf);

Close

Enforce Return After Callback (callback-return)

The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.

function doSomething(err, callback) {
    if (err) {
        return callback(err);
    }
    callback();
}

To prevent calling the callback multiple times it is important to return anytime the callback is triggered outside of the main function body. Neglecting this technique often leads to issues where you do something more than once. For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw a Can't render headers after they are sent to the client. error.

Rule Details

This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately preceding a return statement. This rule decides what is a callback based on the name of the function being called.

Options

The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback, cb, next.

Default callback names

Examples of incorrect code for this rule with the default ["callback", "cb", "next"] option:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        callback(err);
    }
    callback();
}

Examples of correct code for this rule with the default ["callback", "cb", "next"] option:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        return callback(err);
    }
    callback();
}

Supplied callback names

Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]:

/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/

function foo(err, done) {
    if (err) {
        done(err);
    }
    done();
}

function bar(err, send) {
    if (err) {
        send.error(err);
    }
    send.success();
}

Examples of correct code for this rule with the option ["done", "send.error", "send.success"]:

/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/

function foo(err, done) {
    if (err) {
        return done(err);
    }
    done();
}

function bar(err, send) {
    if (err) {
        return send.error(err);
    }
    send.success();
}

Known Limitations

Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:

• false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
• false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)

Passing the callback by reference

The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout).

Example of a false negative when this rule reports correct code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        setTimeout(callback, 0); // this is bad, but WILL NOT warn
    }
    callback();
}

Triggering the callback within a nested function

The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).

Example of a false negative when this rule reports correct code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        process.nextTick(function() {
            return callback(); // this is bad, but WILL NOT warn
        });
    }
    callback();
}

If/else statements

The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if statement.

Example of a false positive when this rule reports incorrect code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        callback(err); // this is fine, but WILL warn
    } else {
        callback();    // this is fine, but WILL warn
    }
}

When Not To Use It

There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.

Further Reading

• The Art Of Node: Callbacks
• Nodejitsu: What are the error conventions?

Related Rules

• [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/

    for (var col in this.frames) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

      for (var row in this.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

        for (var row in this.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

    var ret = undefined;

Close

Disallow Initializing to undefined (no-undef-init)

In JavaScript, a variable that is declared and not initialized to any value automatically gets the value of undefined. For example:

var foo;

console.log(foo === undefined);     // true

It's therefore unnecessary to initialize a variable to undefined, such as:

var foo = undefined;

It's considered a best practice to avoid initializing variables to undefined.

Rule Details

This rule aims to eliminate variable declarations that initialize to undefined.

Examples of incorrect code for this rule:

/*eslint no-undef-init: "error"*/
/*eslint-env es6*/

var foo = undefined;
let bar = undefined;

Examples of correct code for this rule:

/*eslint no-undef-init: "error"*/
/*eslint-env es6*/

var foo;
let bar;
const baz = undefined;

When Not To Use It

There is one situation where initializing to undefined behaves differently than omitting the initialization, and that's when a var declaration occurs inside of a loop. For example:

Example of incorrect code for this rule:

for (i = 0; i < 10; i++) {
    var x = undefined;
    console.log(x);
    x = i;
}

In this case, the var x is hoisted out of the loop, effectively creating:

var x;

for (i = 0; i < 10; i++) {
    x = undefined;
    console.log(x);
    x = i;
}

If you were to remove the initialization, then the behavior of the loop changes:

for (i = 0; i < 10; i++) {
    var x;
    console.log(x);
    x = i;
}

This code is equivalent to:

var x;

for (i = 0; i < 10; i++) {
    console.log(x);
    x = i;
}

This produces a different outcome than defining var x = undefined in the loop, as x is no longer reset to undefined each time through the loop.

If you're using such an initialization inside of a loop, then you should disable this rule.

Example of correct code for this rule, because it is disabled on a specific line:

/*eslint no-undef-init: "error"*/

for (i = 0; i < 10; i++) {
    var x = undefined; // eslint-disable-line no-undef-init
    console.log(x);
    x = i;
}

Related Rules

• [no-undefined](no-undefined.md)
• [no-void](no-void.md) Source: http://eslint.org/docs/rules/

    for (var col in this.frames) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

      alert('nul');

Close

Disallow Use of Alert (no-alert)

JavaScript's alert, confirm, and prompt functions are widely considered to be obtrusive as UI elements and should be replaced by a more appropriate custom UI implementation. Furthermore, alert is often used while debugging code, which should be removed before deployment to production.

alert("here!");

Rule Details

This rule is aimed at catching debugging code that should be removed and popup UI elements that should be replaced with less obtrusive, custom UIs. As such, it will warn when it encounters alert, prompt, and confirm function calls which are not shadowed.

Examples of incorrect code for this rule:

/*eslint no-alert: "error"*/

alert("here!");

confirm("Are you sure?");

prompt("What's your name?", "John Doe");

Examples of correct code for this rule:

/*eslint no-alert: "error"*/

customAlert("Something happened!");

customConfirm("Are you sure?");

customPrompt("Who are you?");

function foo() {
    var alert = myCustomLib.customAlert;
    alert();
}

Related Rules

• [no-console](no-console.md)
• [no-debugger](no-debugger.md) Source: http://eslint.org/docs/rules/

      for (var row in this.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

            for (var i = 0; i < a.length; i++) { this.frames.push(a[i]); }

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

        var row = +this.curframe[2];

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

        var col = +this.curframe[1];

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

    for (var col in this.frames) {

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

        var f = this.frames[col][row];

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

        var col = +this.curframe[1];

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

    for (var col in this.frames) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

            for (var col in this.frames) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

      var mtop = topmargin;

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

      var width = w / cols;

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

          var f = this.frames[col][row];

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

      cb(self, o);

Close

Enforce Return After Callback (callback-return)

The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.

function doSomething(err, callback) {
    if (err) {
        return callback(err);
    }
    callback();
}

To prevent calling the callback multiple times it is important to return anytime the callback is triggered outside of the main function body. Neglecting this technique often leads to issues where you do something more than once. For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw a Can't render headers after they are sent to the client. error.

Rule Details

This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately preceding a return statement. This rule decides what is a callback based on the name of the function being called.

Options

The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback, cb, next.

Default callback names

Examples of incorrect code for this rule with the default ["callback", "cb", "next"] option:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        callback(err);
    }
    callback();
}

Examples of correct code for this rule with the default ["callback", "cb", "next"] option:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        return callback(err);
    }
    callback();
}

Supplied callback names

Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]:

/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/

function foo(err, done) {
    if (err) {
        done(err);
    }
    done();
}

function bar(err, send) {
    if (err) {
        send.error(err);
    }
    send.success();
}

Examples of correct code for this rule with the option ["done", "send.error", "send.success"]:

/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/

function foo(err, done) {
    if (err) {
        return done(err);
    }
    done();
}

function bar(err, send) {
    if (err) {
        return send.error(err);
    }
    send.success();
}

Known Limitations

Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:

• false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
• false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)

Passing the callback by reference

The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout).

Example of a false negative when this rule reports correct code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        setTimeout(callback, 0); // this is bad, but WILL NOT warn
    }
    callback();
}

Triggering the callback within a nested function

The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).

Example of a false negative when this rule reports correct code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        process.nextTick(function() {
            return callback(); // this is bad, but WILL NOT warn
        });
    }
    callback();
}

If/else statements

The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if statement.

Example of a false positive when this rule reports incorrect code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        callback(err); // this is fine, but WILL warn
    } else {
        callback();    // this is fine, but WILL warn
    }
}

When Not To Use It

There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.

Further Reading

• The Art Of Node: Callbacks
• Nodejitsu: What are the error conventions?

Related Rules

• [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/

      var newname = prompt('title');

Close

Disallow Use of Alert (no-alert)

JavaScript's alert, confirm, and prompt functions are widely considered to be obtrusive as UI elements and should be replaced by a more appropriate custom UI implementation. Furthermore, alert is often used while debugging code, which should be removed before deployment to production.

alert("here!");

Rule Details

This rule is aimed at catching debugging code that should be removed and popup UI elements that should be replaced with less obtrusive, custom UIs. As such, it will warn when it encounters alert, prompt, and confirm function calls which are not shadowed.

Examples of incorrect code for this rule:

/*eslint no-alert: "error"*/

alert("here!");

confirm("Are you sure?");

prompt("What's your name?", "John Doe");

Examples of correct code for this rule:

/*eslint no-alert: "error"*/

customAlert("Something happened!");

customConfirm("Are you sure?");

customPrompt("Who are you?");

function foo() {
    var alert = myCustomLib.customAlert;
    alert();
}

Related Rules

• [no-console](no-console.md)
• [no-debugger](no-debugger.md) Source: http://eslint.org/docs/rules/

    for (var col in this.frames) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

            var a = this.frames.splice(col).slice(1);

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

      for (var col in this.frames) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

      var height = (h - topmargin) / rows;

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

        var col = +this.curframe[1];

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

          var f = this.frames[col][0];

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

    var x = document.createElement('p');

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

    var prev = undefined;

Close

Disallow Initializing to undefined (no-undef-init)

In JavaScript, a variable that is declared and not initialized to any value automatically gets the value of undefined. For example:

var foo;

console.log(foo === undefined);     // true

It's therefore unnecessary to initialize a variable to undefined, such as:

var foo = undefined;

It's considered a best practice to avoid initializing variables to undefined.

Rule Details

This rule aims to eliminate variable declarations that initialize to undefined.

Examples of incorrect code for this rule:

/*eslint no-undef-init: "error"*/
/*eslint-env es6*/

var foo = undefined;
let bar = undefined;

Examples of correct code for this rule:

/*eslint no-undef-init: "error"*/
/*eslint-env es6*/

var foo;
let bar;
const baz = undefined;

When Not To Use It

There is one situation where initializing to undefined behaves differently than omitting the initialization, and that's when a var declaration occurs inside of a loop. For example:

Example of incorrect code for this rule:

for (i = 0; i < 10; i++) {
    var x = undefined;
    console.log(x);
    x = i;
}

In this case, the var x is hoisted out of the loop, effectively creating:

var x;

for (i = 0; i < 10; i++) {
    x = undefined;
    console.log(x);
    x = i;
}

If you were to remove the initialization, then the behavior of the loop changes:

for (i = 0; i < 10; i++) {
    var x;
    console.log(x);
    x = i;
}

This code is equivalent to:

var x;

for (i = 0; i < 10; i++) {
    console.log(x);
    x = i;
}

This produces a different outcome than defining var x = undefined in the loop, as x is no longer reset to undefined each time through the loop.

If you're using such an initialization inside of a loop, then you should disable this rule.

Example of correct code for this rule, because it is disabled on a specific line:

/*eslint no-undef-init: "error"*/

for (i = 0; i < 10; i++) {
    var x = undefined; // eslint-disable-line no-undef-init
    console.log(x);
    x = i;
}

Related Rules

• [no-undefined](no-undefined.md)
• [no-void](no-void.md) Source: http://eslint.org/docs/rules/

            for (var col in this.frames) {

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

    for (var col in this.frames) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

        var b = this.frames.slice(col + 1);

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

      cb(self, nf);

Close

Enforce Return After Callback (callback-return)

The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.

function doSomething(err, callback) {
    if (err) {
        return callback(err);
    }
    callback();
}

To prevent calling the callback multiple times it is important to return anytime the callback is triggered outside of the main function body. Neglecting this technique often leads to issues where you do something more than once. For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw a Can't render headers after they are sent to the client. error.

Rule Details

This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately preceding a return statement. This rule decides what is a callback based on the name of the function being called.

Options

The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback, cb, next.

Default callback names

Examples of incorrect code for this rule with the default ["callback", "cb", "next"] option:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        callback(err);
    }
    callback();
}

Examples of correct code for this rule with the default ["callback", "cb", "next"] option:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        return callback(err);
    }
    callback();
}

Supplied callback names

Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]:

/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/

function foo(err, done) {
    if (err) {
        done(err);
    }
    done();
}

function bar(err, send) {
    if (err) {
        send.error(err);
    }
    send.success();
}

Examples of correct code for this rule with the option ["done", "send.error", "send.success"]:

/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/

function foo(err, done) {
    if (err) {
        return done(err);
    }
    done();
}

function bar(err, send) {
    if (err) {
        return send.error(err);
    }
    send.success();
}

Known Limitations

Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:

• false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
• false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)

Passing the callback by reference

The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout).

Example of a false negative when this rule reports correct code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        setTimeout(callback, 0); // this is bad, but WILL NOT warn
    }
    callback();
}

Triggering the callback within a nested function

The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).

Example of a false negative when this rule reports correct code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        process.nextTick(function() {
            return callback(); // this is bad, but WILL NOT warn
        });
    }
    callback();
}

If/else statements

The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if statement.

Example of a false positive when this rule reports incorrect code:

/*eslint callback-return: "error"*/

function foo(err, callback) {
    if (err) {
        callback(err); // this is fine, but WILL warn
    } else {
        callback();    // this is fine, but WILL warn
    }
}

When Not To Use It

There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.

Further Reading

• The Art Of Node: Callbacks
• Nodejitsu: What are the error conventions?

Related Rules

• [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/

          alert('Cant find frame for ' + name);

Close

Disallow Use of Alert (no-alert)

JavaScript's alert, confirm, and prompt functions are widely considered to be obtrusive as UI elements and should be replaced by a more appropriate custom UI implementation. Furthermore, alert is often used while debugging code, which should be removed before deployment to production.

alert("here!");

Rule Details

This rule is aimed at catching debugging code that should be removed and popup UI elements that should be replaced with less obtrusive, custom UIs. As such, it will warn when it encounters alert, prompt, and confirm function calls which are not shadowed.

Examples of incorrect code for this rule:

/*eslint no-alert: "error"*/

alert("here!");

confirm("Are you sure?");

prompt("What's your name?", "John Doe");

Examples of correct code for this rule:

/*eslint no-alert: "error"*/

customAlert("Something happened!");

customConfirm("Are you sure?");

customPrompt("Who are you?");

function foo() {
    var alert = myCustomLib.customAlert;
    alert();
}

Related Rules

• [no-console](no-console.md)
• [no-debugger](no-debugger.md) Source: http://eslint.org/docs/rules/

      for (var row in this.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

    for (var col in this.frames) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

          var f = this.frames[col];

Close

disallow variable redeclaration (no-redeclare)

In JavaScript, it's possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

Examples of incorrect code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
var a = 10;

Examples of correct code for this rule:

/*eslint no-redeclare: "error"*/

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false. If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number...

builtinGlobals

Examples of incorrect code for the { "builtinGlobals": true } option:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared. Source: http://eslint.org/docs/rules/

      for (var row in this.frames[col]) {

Close

Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

    (function (self, name) {

Close

Require IIFEs to be Wrapped (wrap-iife)

You can immediately invoke function expressions, but not function declarations. A common technique to create an immediately-invoked function expression (IIFE) is to wrap a function declaration in parentheses. The opening parentheses causes the contained function to be parsed as an expression, rather than a declaration.

// function expression could be unwrapped
var x = function () { return { y: 1 };}();

// function declaration must be wrapped
function () { /* side effects */ }(); // SyntaxError

Rule Details

This rule requires all immediately-invoked function expressions to be wrapped in parentheses.

Options

This rule has two options, a string option and an object option.

String option:

• "outside" enforces always wrapping the call expression. The default is "outside".
• "inside" enforces always wrapping the function expression.
• "any" enforces always wrapping, but allows either style.

Object option:

• "functionPrototypeMethods": true additionally enforces wrapping function expressions invoked using .call and .apply. The default is false.

outside

Examples of incorrect code for the default "outside" option:

/*eslint wrap-iife: ["error", "outside"]*/

var x = function () { return { y: 1 };}(); // unwrapped
var x = (function () { return { y: 1 };})(); // wrapped function expression

Examples of correct code for the default "outside" option:

/*eslint wrap-iife: ["error", "outside"]*/

var x = (function () { return { y: 1 };}()); // wrapped call expression

inside

Examples of incorrect code for the "inside" option:

/*eslint wrap-iife: ["error", "inside"]*/

var x = function () { return { y: 1 };}(); // unwrapped
var x = (function () { return { y: 1 };}()); // wrapped call expression

Examples of correct code for the "inside" option:

/*eslint wrap-iife: ["error", "inside"]*/

var x = (function () { return { y: 1 };})(); // wrapped function expression

any

Examples of incorrect code for the "any" option:

/*eslint wrap-iife: ["error", "any"]*/

var x = function () { return { y: 1 };}(); // unwrapped

Examples of correct code for the "any" option:

/*eslint wrap-iife: ["error", "any"]*/

var x = (function () { return { y: 1 };}()); // wrapped call expression
var x = (function () { return { y: 1 };})(); // wrapped function expression

functionPrototypeMethods

Examples of incorrect code for this rule with the "inside", { "functionPrototypeMethods": true } options:

/* eslint wrap-iife: [2, "inside", { functionPrototypeMethods: true }] */

var x = function(){ foo(); }()
var x = (function(){ foo(); }())
var x = function(){ foo(); }.call(bar)
var x = (function(){ foo(); }.call(bar))

Examples of correct code for this rule with the "inside", { "functionPrototypeMethods": true } options:

/* eslint wrap-iife: [2, "inside", { functionPrototypeMethods: true }] */

var x = (function(){ foo(); })()
var x = (function(){ foo(); }).call(bar)

Source: http://eslint.org/docs/rules/

      for (var row in this.frames[col]) {
        var f = this.frames[col][row];
        f.mh = false;
      }

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 51.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

      for (var row in this.frames[col]) {
        var f = this.frames[col][row];
        f.selected = false;
      }

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 51.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

          if (f) {
            this.select_frame(f.name);
            this.curframe = [f, col, 0];
            this.run();
          }

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 47.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

          if (f) {
            this.select_frame(f.name);
            this.curframe = [f, col, 0];
            this.run();
          }

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 47.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

            for (var i = 0; i < a.length; i++) { this.frames.push(a[i]); }

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 46.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

        for (var i = 0; i < d.length; i++) { this.frames.push(d[i]); }

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 46.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76