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 65.

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

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 65.

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

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

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

Close

require or disallow trailing commas (comma-dangle)

Trailing commas in object literals are valid according to the ECMAScript 5 (and ECMAScript 3!) spec. However, IE8 (when not in IE8 document mode) and below will throw an error when it encounters trailing commas in JavaScript.

var foo = {
    bar: "baz",
    qux: "quux",
};

Trailing commas simplify adding and removing items to objects and arrays, since only the lines you are modifying must be touched. Another argument in favor of trailing commas is that it improves the clarity of diffs when an item is added or removed from an object or array:

Less clear:

var foo = {
-    bar: "baz",
-    qux: "quux"
+    bar: "baz"
 };

More clear:

var foo = {
     bar: "baz",
-    qux: "quux",
 };

Rule Details

This rule enforces consistent use of trailing commas in object and array literals.

Options

This rule has a string option or an object option:

{
    "comma-dangle": ["error", "never"],
    // or
    "comma-dangle": ["error", {
        "arrays": "never",
        "objects": "never",
        "imports": "never",
        "exports": "never",
        "functions": "ignore",
    }]
}

• "never" (default) disallows trailing commas
• "always" requires trailing commas
• "always-multiline" requires trailing commas when the last element or property is in a different line than the closing ] or } and disallows trailing commas when the last element or property is on the same line as the closing ] or }
• "only-multiline" allows (but does not require) trailing commas when the last element or property is in a different line than the closing ] or } and disallows trailing commas when the last element or property is on the same line as the closing ] or }

Trailing commas in function declarations and function calls are valid syntax since ECMAScript 2017; however, the string option does not check these situations for backwards compatibility.

You can also use an object option to configure this rule for each type of syntax. Each of the following options can be set to "never", "always", "always-multiline", "only-multiline", or "ignore". The default for each option is "never" unless otherwise specified.

• arrays is for array literals and array patterns of destructuring. (e.g. let [a,] = [1,];)
• objects is for object literals and object patterns of destructuring. (e.g. let {a,} = {a: 1};)
• imports is for import declarations of ES Modules. (e.g. import {a,} from "foo";)
• exports is for export declarations of ES Modules. (e.g. export {a,};)
• functions is for function declarations and function calls. (e.g. (function(a,){ })(b,);)
  functions is set to "ignore" by default for consistency with the string option.

never

Examples of incorrect code for this rule with the default "never" option:

/*eslint comma-dangle: ["error", "never"]*/
 
var foo = {
    bar: "baz",
    qux: "quux",
};
 
var arr = [1,2,];
 
foo({
  bar: "baz",
  qux: "quux",
});

Examples of correct code for this rule with the default "never" option:

/*eslint comma-dangle: ["error", "never"]*/
 
var foo = {
    bar: "baz",
    qux: "quux"
};
 
var arr = [1,2];
 
foo({
  bar: "baz",
  qux: "quux"
});

always

Examples of incorrect code for this rule with the "always" option:

/*eslint comma-dangle: ["error", "always"]*/
 
var foo = {
    bar: "baz",
    qux: "quux"
};
 
var arr = [1,2];
 
foo({
  bar: "baz",
  qux: "quux"
});

Examples of correct code for this rule with the "always" option:

/*eslint comma-dangle: ["error", "always"]*/
 
var foo = {
    bar: "baz",
    qux: "quux",
};
 
var arr = [1,2,];
 
foo({
  bar: "baz",
  qux: "quux",
});

always-multiline

Examples of incorrect code for this rule with the "always-multiline" option:

/*eslint comma-dangle: ["error", "always-multiline"]*/
 
var foo = {
    bar: "baz",
    qux: "quux"
};
 
var foo = { bar: "baz", qux: "quux", };
 
var arr = [1,2,];
 
var arr = [1,
    2,];
 
var arr = [
    1,
    2
];
 
foo({
  bar: "baz",
  qux: "quux"
});

Examples of correct code for this rule with the "always-multiline" option:

/*eslint comma-dangle: ["error", "always-multiline"]*/
 
var foo = {
    bar: "baz",
    qux: "quux",
};
 
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
 
var arr = [1,
    2];
 
var arr = [
    1,
    2,
];
 
foo({
  bar: "baz",
  qux: "quux",
});

only-multiline

Examples of incorrect code for this rule with the "only-multiline" option:

/*eslint comma-dangle: ["error", "only-multiline"]*/
 
var foo = { bar: "baz", qux: "quux", };
 
var arr = [1,2,];
 
var arr = [1,
    2,];

Examples of correct code for this rule with the "only-multiline" option:

/*eslint comma-dangle: ["error", "only-multiline"]*/
 
var foo = {
    bar: "baz",
    qux: "quux",
};
 
var foo = {
    bar: "baz",
    qux: "quux"
};
 
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
 
var arr = [1,
    2];
 
var arr = [
    1,
    2,
];
 
var arr = [
    1,
    2
];
 
foo({
  bar: "baz",
  qux: "quux",
});
 
foo({
  bar: "baz",
  qux: "quux"
});

functions

Examples of incorrect code for this rule with the {"functions": "never"} option:

/*eslint comma-dangle: ["error", {"functions": "never"}]*/
 
function foo(a, b,) {
}
 
foo(a, b,);
new foo(a, b,);

Examples of correct code for this rule with the {"functions": "never"} option:

/*eslint comma-dangle: ["error", {"functions": "never"}]*/
 
function foo(a, b) {
}
 
foo(a, b);
new foo(a, b);

Examples of incorrect code for this rule with the {"functions": "always"} option:

/*eslint comma-dangle: ["error", {"functions": "always"}]*/
 
function foo(a, b) {
}
 
foo(a, b);
new foo(a, b);

Examples of correct code for this rule with the {"functions": "always"} option:

/*eslint comma-dangle: ["error", {"functions": "always"}]*/
 
function foo(a, b,) {
}
 
foo(a, b,);
new foo(a, b,);

When Not To Use It

You can turn this rule off if you are not concerned with dangling commas. Source: http://eslint.org/docs/rules/

Close

This cop checks for assignments in the conditions of if/while/until.

Example:

# bad
 
if some_var = true
  do_something
end

Example:

# good
 
if some_var == true
  do_something
end

Close

disallow unnecessary semicolons (no-extra-semi)

Typing mistakes and misunderstandings about where semicolons are required can lead to semicolons that are unnecessary. While not technically an error, extra semicolons can cause confusion when reading code.

Rule Details

This rule disallows unnecessary semicolons.

Examples of incorrect code for this rule:

/*eslint no-extra-semi: "error"*/
 
var x = 5;;
 
function foo() {
    // code
};

Examples of correct code for this rule:

/*eslint no-extra-semi: "error"*/
 
var x = 5;
 
var foo = function() {
    // code
};

When Not To Use It

If you intentionally use extra semicolons then you can disable this rule.

Related Rules

• [semi](semi.md)
• [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/

Close

disallow assignment operators in conditional statements (no-cond-assign)

In conditional statements, it is very easy to mistype a comparison operator (such as ==) as an assignment operator (such as =). For example:

// Check the user's job title
if (user.jobTitle = "manager") {
    // user.jobTitle is now incorrect
}

There are valid reasons to use assignment operators in conditional statements. However, it can be difficult to tell whether a specific assignment was intentional.

Rule Details

This rule disallows ambiguous assignment operators in test conditions of if, for, while, and do...while statements.

Options

This rule has a string option:

• "except-parens" (default) allows assignments in test conditions only if they are enclosed in parentheses (for example, to allow reassigning a variable in the test of a while or do...while loop)
• "always" disallows all assignments in test conditions

except-parens

Examples of incorrect code for this rule with the default "except-parens" option:

/*eslint no-cond-assign: "error"*/
 
// Unintentional assignment
var x;
if (x = 0) {
    var b = 1;
}
 
// Practical example that is similar to an error
function setHeight(someNode) {
    "use strict";
    do {
        someNode.height = "100px";
    } while (someNode = someNode.parentNode);
}

Examples of correct code for this rule with the default "except-parens" option:

/*eslint no-cond-assign: "error"*/
 
// Assignment replaced by comparison
var x;
if (x === 0) {
    var b = 1;
}
 
// Practical example that wraps the assignment in parentheses
function setHeight(someNode) {
    "use strict";
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode));
}
 
// Practical example that wraps the assignment and tests for 'null'
function setHeight(someNode) {
    "use strict";
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode) !== null);
}

always

Examples of incorrect code for this rule with the "always" option:

/*eslint no-cond-assign: ["error", "always"]*/
 
// Unintentional assignment
var x;
if (x = 0) {
    var b = 1;
}
 
// Practical example that is similar to an error
function setHeight(someNode) {
    "use strict";
    do {
        someNode.height = "100px";
    } while (someNode = someNode.parentNode);
}
 
// Practical example that wraps the assignment in parentheses
function setHeight(someNode) {
    "use strict";
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode));
}
 
// Practical example that wraps the assignment and tests for 'null'
function setHeight(someNode) {
    "use strict";
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode) !== null);
}

Examples of correct code for this rule with the "always" option:

/*eslint no-cond-assign: ["error", "always"]*/
 
// Assignment replaced by comparison
var x;
if (x === 0) {
    var b = 1;
}

Related Rules

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

Close

require or disallow trailing commas (comma-dangle)

Trailing commas in object literals are valid according to the ECMAScript 5 (and ECMAScript 3!) spec. However, IE8 (when not in IE8 document mode) and below will throw an error when it encounters trailing commas in JavaScript.

var foo = {
    bar: "baz",
    qux: "quux",
};

Trailing commas simplify adding and removing items to objects and arrays, since only the lines you are modifying must be touched. Another argument in favor of trailing commas is that it improves the clarity of diffs when an item is added or removed from an object or array:

Less clear:

var foo = {
-    bar: "baz",
-    qux: "quux"
+    bar: "baz"
 };

More clear:

var foo = {
     bar: "baz",
-    qux: "quux",
 };

Rule Details

This rule enforces consistent use of trailing commas in object and array literals.

Options

This rule has a string option or an object option:

{
    "comma-dangle": ["error", "never"],
    // or
    "comma-dangle": ["error", {
        "arrays": "never",
        "objects": "never",
        "imports": "never",
        "exports": "never",
        "functions": "ignore",
    }]
}

• "never" (default) disallows trailing commas
• "always" requires trailing commas
• "always-multiline" requires trailing commas when the last element or property is in a different line than the closing ] or } and disallows trailing commas when the last element or property is on the same line as the closing ] or }
• "only-multiline" allows (but does not require) trailing commas when the last element or property is in a different line than the closing ] or } and disallows trailing commas when the last element or property is on the same line as the closing ] or }

Trailing commas in function declarations and function calls are valid syntax since ECMAScript 2017; however, the string option does not check these situations for backwards compatibility.

You can also use an object option to configure this rule for each type of syntax. Each of the following options can be set to "never", "always", "always-multiline", "only-multiline", or "ignore". The default for each option is "never" unless otherwise specified.

• arrays is for array literals and array patterns of destructuring. (e.g. let [a,] = [1,];)
• objects is for object literals and object patterns of destructuring. (e.g. let {a,} = {a: 1};)
• imports is for import declarations of ES Modules. (e.g. import {a,} from "foo";)
• exports is for export declarations of ES Modules. (e.g. export {a,};)
• functions is for function declarations and function calls. (e.g. (function(a,){ })(b,);)
  functions is set to "ignore" by default for consistency with the string option.

never

Examples of incorrect code for this rule with the default "never" option:

/*eslint comma-dangle: ["error", "never"]*/
 
var foo = {
    bar: "baz",
    qux: "quux",
};
 
var arr = [1,2,];
 
foo({
  bar: "baz",
  qux: "quux",
});

Examples of correct code for this rule with the default "never" option:

/*eslint comma-dangle: ["error", "never"]*/
 
var foo = {
    bar: "baz",
    qux: "quux"
};
 
var arr = [1,2];
 
foo({
  bar: "baz",
  qux: "quux"
});

always

Examples of incorrect code for this rule with the "always" option:

/*eslint comma-dangle: ["error", "always"]*/
 
var foo = {
    bar: "baz",
    qux: "quux"
};
 
var arr = [1,2];
 
foo({
  bar: "baz",
  qux: "quux"
});

Examples of correct code for this rule with the "always" option:

/*eslint comma-dangle: ["error", "always"]*/
 
var foo = {
    bar: "baz",
    qux: "quux",
};
 
var arr = [1,2,];
 
foo({
  bar: "baz",
  qux: "quux",
});

always-multiline

Examples of incorrect code for this rule with the "always-multiline" option:

/*eslint comma-dangle: ["error", "always-multiline"]*/
 
var foo = {
    bar: "baz",
    qux: "quux"
};
 
var foo = { bar: "baz", qux: "quux", };
 
var arr = [1,2,];
 
var arr = [1,
    2,];
 
var arr = [
    1,
    2
];
 
foo({
  bar: "baz",
  qux: "quux"
});

Examples of correct code for this rule with the "always-multiline" option:

/*eslint comma-dangle: ["error", "always-multiline"]*/
 
var foo = {
    bar: "baz",
    qux: "quux",
};
 
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
 
var arr = [1,
    2];
 
var arr = [
    1,
    2,
];
 
foo({
  bar: "baz",
  qux: "quux",
});

only-multiline

Examples of incorrect code for this rule with the "only-multiline" option:

/*eslint comma-dangle: ["error", "only-multiline"]*/
 
var foo = { bar: "baz", qux: "quux", };
 
var arr = [1,2,];
 
var arr = [1,
    2,];

Examples of correct code for this rule with the "only-multiline" option:

/*eslint comma-dangle: ["error", "only-multiline"]*/
 
var foo = {
    bar: "baz",
    qux: "quux",
};
 
var foo = {
    bar: "baz",
    qux: "quux"
};
 
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
 
var arr = [1,
    2];
 
var arr = [
    1,
    2,
];
 
var arr = [
    1,
    2
];
 
foo({
  bar: "baz",
  qux: "quux",
});
 
foo({
  bar: "baz",
  qux: "quux"
});

functions

Examples of incorrect code for this rule with the {"functions": "never"} option:

/*eslint comma-dangle: ["error", {"functions": "never"}]*/
 
function foo(a, b,) {
}
 
foo(a, b,);
new foo(a, b,);

Examples of correct code for this rule with the {"functions": "never"} option:

/*eslint comma-dangle: ["error", {"functions": "never"}]*/
 
function foo(a, b) {
}
 
foo(a, b);
new foo(a, b);

Examples of incorrect code for this rule with the {"functions": "always"} option:

/*eslint comma-dangle: ["error", {"functions": "always"}]*/
 
function foo(a, b) {
}
 
foo(a, b);
new foo(a, b);

Examples of correct code for this rule with the {"functions": "always"} option:

/*eslint comma-dangle: ["error", {"functions": "always"}]*/
 
function foo(a, b,) {
}
 
foo(a, b,);
new foo(a, b,);

When Not To Use It

You can turn this rule off if you are not concerned with dangling commas. Source: http://eslint.org/docs/rules/