const applyActions = (socketMessage, data) => {
    if (data.tap) {
        socketMessage.taps = [{
            type: data.tap,
            ...(data.tapDuration ? {duration: data.tapDuration} : {}),

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

function readConfigFile(filePath) {
    const extension = path.extname(filePath);
    if (extension === '.js') {
        if (!path.isAbsolute(filePath)) {
            // ensure correct handling of relative paths, we want to prevent searching in __dirname

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

const openDeepLinkFactory = (classInstance) => {
    const toJSON = (data) => ({
        type: getRequestType(data, false),
        request: {
            type: 'openDeepLink',

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

    const rcConfig = readRcConfig(argv.baseConfigFile || argv.configFile);

Close

require or disallow an empty line after variable declarations (newline-after-var)

This rule was deprecated in ESLint v4.0.0 and replaced by the [padding-line-between-statements](padding-line-between-statements.md) rule.

As of today there is no consistency in separating variable declarations from the rest of the code. Some developers leave an empty line between var statements and the rest of the code like:

var foo;

// do something with foo

Whereas others don't leave any empty newlines at all.

var foo;
// do something with foo

The problem is when these developers work together in a project. This rule enforces a coding style where empty newlines are allowed or disallowed after var, let, or const statements. It helps the code to look consistent across the entire project.

Rule Details

This rule enforces a coding style where empty lines are required or disallowed after var, let, or const statements to achieve a consistent coding style across the project.

Options

This rule has a string option:

• "always" (default) requires an empty line after var, let, or const

Comments on a line directly after var statements are treated like additional var statements.

• "never" disallows empty lines after var, let, or const

always

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

/*eslint newline-after-var: ["error", "always"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";
console.log(greet, name);

let greet = "hello,",
    name = "world";
console.log(greet, name);

var greet = "hello,";
const NAME = "world";
console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");
console.log(greet, name);

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

/*eslint newline-after-var: ["error", "always"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";

console.log(greet, name);

let greet = "hello,",
    name = "world";

console.log(greet, name);

var greet = "hello,";
const NAME = "world";

console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");

console.log(greet, name);

never

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

/*eslint newline-after-var: ["error", "never"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";

console.log(greet, name);

let greet = "hello,",
    name = "world";

console.log(greet, name);

var greet = "hello,";
const NAME = "world";

console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");

console.log(greet, name);

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

/*eslint newline-after-var: ["error", "never"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";
console.log(greet, name);

let greet = "hello,",
    name = "world";
console.log(greet, name);

var greet = "hello,";
const NAME = "world";
console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");
console.log(greet, name);

Source: http://eslint.org/docs/rules/

const elementFactory = (classInstance, video) => {

Close

Disallow Unused Variables (no-unused-vars)

Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

Rule Details

This rule is aimed at eliminating unused variables, functions, and parameters of functions.

A variable is considered to be used if any of the following are true:

• It represents a function that is called (doSomething())
• It is read (var y = x)
• It is passed into a function as an argument (doSomething(x))
• It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

A variable is not considered to be used if it is only ever assigned to (var x = 5) or declared.

Examples of incorrect code for this rule:

/*eslint no-unused-vars: "error"*/
/*global some_unused_var*/

// It checks variables you have defined as global
some_unused_var = 42;

var x;

// Write-only variables are not considered as used.
var y = 10;
y = 5;

// A read for a modification of itself is not considered as used.
var z = 0;
z = z + 1;

// By default, unused arguments cause warnings.
(function(foo) {
    return 5;
})();

// Unused recursive functions also cause warnings.
function fact(n) {
    if (n < 2) return 1;
    return n * fact(n - 1);
}

// When a function definition destructures an array, unused entries from the array also cause warnings.
function getY([x, y]) {
    return y;
}

Examples of correct code for this rule:

/*eslint no-unused-vars: "error"*/

var x = 10;
alert(x);

// foo is considered used here
myFunc(function foo() {
    // ...
}.bind(this));

(function(foo) {
    return foo;
})();

var myFunc;
myFunc = setTimeout(function() {
    // myFunc is considered used
    myFunc();
}, 50);

// Only the second argument from the descructured array is used.
function getY([, y]) {
    return y;
}

exported

In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

Note that /* exported */ has no effect for any of the following:

• when the environment is node or commonjs
• when parserOptions.sourceType is module
• when ecmaFeatures.globalReturn is true

The line comment // exported variableName will not work as exported is not line-specific.

Examples of correct code for /* exported variableName */ operation:

/* exported global_var */

var global_var = 42;

Options

This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

By default this rule is enabled with all option for variables and after-used for arguments.

{
    "rules": {
        "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
    }
}

vars

The vars option has two settings:

• all checks all variables for usage, including those in the global scope. This is the default setting.
• local checks only that locally-declared variables are used but will allow global variables to be unused.

vars: local

Examples of correct code for the { "vars": "local" } option:

/*eslint no-unused-vars: ["error", { "vars": "local" }]*/
/*global some_unused_var */

some_unused_var = 42;

varsIgnorePattern

The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

/*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/

var firstVarIgnored = 1;
var secondVar = 2;
console.log(secondVar);

args

The args option has three settings:

• after-used - only the last argument must be used. This allows you, for instance, to have two named parameters to a function and as long as you use the second argument, ESLint will not warn you about the first. This is the default setting.
• all - all named arguments must be used.
• none - do not check arguments.

args: after-used

Examples of incorrect code for the default { "args": "after-used" } option:

/*eslint no-unused-vars: ["error", { "args": "after-used" }]*/

// 1 error
// "baz" is defined but never used
(function(foo, bar, baz) {
    return bar;
})();

Examples of correct code for the default { "args": "after-used" } option:

/*eslint no-unused-vars: ["error", {"args": "after-used"}]*/

(function(foo, bar, baz) {
    return baz;
})();

args: all

Examples of incorrect code for the { "args": "all" } option:

/*eslint no-unused-vars: ["error", { "args": "all" }]*/

// 2 errors
// "foo" is defined but never used
// "baz" is defined but never used
(function(foo, bar, baz) {
    return bar;
})();

args: none

Examples of correct code for the { "args": "none" } option:

/*eslint no-unused-vars: ["error", { "args": "none" }]*/

(function(foo, bar, baz) {
    return bar;
})();

ignoreRestSiblings

The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

Examples of correct code for the { "ignoreRestSiblings": true } option:

/*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
// 'type' is ignored because it has a rest property sibling.
var { type, ...coords } = data;

argsIgnorePattern

The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

Examples of correct code for the { "argsIgnorePattern": "^_" } option:

/*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/

function foo(x, _y) {
    return x + 1;
}
foo();

caughtErrors

The caughtErrors option is used for catch block arguments validation.

It has two settings:

• none - do not check error objects. This is the default setting.
• all - all named arguments must be used.

caughtErrors: none

Not specifying this rule is equivalent of assigning it to none.

Examples of correct code for the { "caughtErrors": "none" } option:

/*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/

try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrors: all

Examples of incorrect code for the { "caughtErrors": "all" } option:

/*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/

// 1 error
// "err" is defined but never used
try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrorsIgnorePattern

The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

/*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/

try {
    //...
} catch (ignoreErr) {
    console.error("errors");
}

When Not To Use It

If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

    const extension = path.extname(filePath);

Close

require or disallow an empty line after variable declarations (newline-after-var)

This rule was deprecated in ESLint v4.0.0 and replaced by the [padding-line-between-statements](padding-line-between-statements.md) rule.

As of today there is no consistency in separating variable declarations from the rest of the code. Some developers leave an empty line between var statements and the rest of the code like:

var foo;

// do something with foo

Whereas others don't leave any empty newlines at all.

var foo;
// do something with foo

The problem is when these developers work together in a project. This rule enforces a coding style where empty newlines are allowed or disallowed after var, let, or const statements. It helps the code to look consistent across the entire project.

Rule Details

This rule enforces a coding style where empty lines are required or disallowed after var, let, or const statements to achieve a consistent coding style across the project.

Options

This rule has a string option:

• "always" (default) requires an empty line after var, let, or const

Comments on a line directly after var statements are treated like additional var statements.

• "never" disallows empty lines after var, let, or const

always

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

/*eslint newline-after-var: ["error", "always"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";
console.log(greet, name);

let greet = "hello,",
    name = "world";
console.log(greet, name);

var greet = "hello,";
const NAME = "world";
console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");
console.log(greet, name);

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

/*eslint newline-after-var: ["error", "always"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";

console.log(greet, name);

let greet = "hello,",
    name = "world";

console.log(greet, name);

var greet = "hello,";
const NAME = "world";

console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");

console.log(greet, name);

never

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

/*eslint newline-after-var: ["error", "never"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";

console.log(greet, name);

let greet = "hello,",
    name = "world";

console.log(greet, name);

var greet = "hello,";
const NAME = "world";

console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");

console.log(greet, name);

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

/*eslint newline-after-var: ["error", "never"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";
console.log(greet, name);

let greet = "hello,",
    name = "world";
console.log(greet, name);

var greet = "hello,";
const NAME = "world";
console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");
console.log(greet, name);

Source: http://eslint.org/docs/rules/

        return require(filePath);

Close

require an empty line before return statements (newline-before-return)

This rule was deprecated in ESLint v4.0.0 and replaced by the [padding-line-between-statements](padding-line-between-statements.md) rule.

There is no hard and fast rule about whether empty lines should precede return statements in JavaScript. However, clearly delineating where a function is returning can greatly increase the readability and clarity of the code. For example:

function foo(bar) {
  var baz = 'baz';
  if (!bar) {
    bar = baz;
    return bar;
  }
  return bar;
}

Adding newlines visibly separates the return statements from the previous lines, making it clear where the function exits and what value it returns:

function foo(bar) {
  var baz = 'baz';

  if (!bar) {
    bar = baz;

    return bar;
  }

  return bar;
}

Rule Details

This rule requires an empty line before return statements to increase code clarity, except when the return is alone inside a statement group (such as an if statement). In the latter case, the return statement does not need to be delineated by virtue of it being alone. Comments are ignored and do not count as empty lines.

Examples of incorrect code for this rule:

/*eslint newline-before-return: "error"*/

function foo(bar) {
    if (!bar) {
        return;
    }
    return bar;
}

function foo(bar) {
    if (!bar) {
        return;
    }
    /* multi-line
    comment */
    return bar;
}

Examples of correct code for this rule:

/*eslint newline-before-return: "error"*/

function foo() {
    return;
}

function foo() {

    return;
}

function foo(bar) {
    if (!bar) return;
}

function foo(bar) {
    if (!bar) { return };
}

function foo(bar) {
    if (!bar) {
        return;
    }
}

function foo(bar) {
    if (!bar) {
        return;
    }

    return bar;
}

function foo(bar) {
    if (!bar) {

        return;
    }
}

function foo() {

    // comment
    return;
}

When Not To Use It

You can safely disable this rule if you do not have any strict conventions about whitespace before return statements.

Related Rules

• [newline-after-var](newline-after-var.md) Source: http://eslint.org/docs/rules/

        const response = await request([endpoints.device, {deviceId}], authorizeHttp, function(res) {

Close

require or disallow an empty line after variable declarations (newline-after-var)

This rule was deprecated in ESLint v4.0.0 and replaced by the [padding-line-between-statements](padding-line-between-statements.md) rule.

As of today there is no consistency in separating variable declarations from the rest of the code. Some developers leave an empty line between var statements and the rest of the code like:

var foo;

// do something with foo

Whereas others don't leave any empty newlines at all.

var foo;
// do something with foo

The problem is when these developers work together in a project. This rule enforces a coding style where empty newlines are allowed or disallowed after var, let, or const statements. It helps the code to look consistent across the entire project.

Rule Details

This rule enforces a coding style where empty lines are required or disallowed after var, let, or const statements to achieve a consistent coding style across the project.

Options

This rule has a string option:

• "always" (default) requires an empty line after var, let, or const

Comments on a line directly after var statements are treated like additional var statements.

• "never" disallows empty lines after var, let, or const

always

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

/*eslint newline-after-var: ["error", "always"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";
console.log(greet, name);

let greet = "hello,",
    name = "world";
console.log(greet, name);

var greet = "hello,";
const NAME = "world";
console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");
console.log(greet, name);

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

/*eslint newline-after-var: ["error", "always"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";

console.log(greet, name);

let greet = "hello,",
    name = "world";

console.log(greet, name);

var greet = "hello,";
const NAME = "world";

console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");

console.log(greet, name);

never

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

/*eslint newline-after-var: ["error", "never"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";

console.log(greet, name);

let greet = "hello,",
    name = "world";

console.log(greet, name);

var greet = "hello,";
const NAME = "world";

console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");

console.log(greet, name);

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

/*eslint newline-after-var: ["error", "never"]*/
/*eslint-env es6*/

var greet = "hello,",
    name = "world";
console.log(greet, name);

let greet = "hello,",
    name = "world";
console.log(greet, name);

var greet = "hello,";
const NAME = "world";
console.log(greet, NAME);

var greet = "hello,";
var name = "world";
// var name = require("world");
console.log(greet, name);

Source: http://eslint.org/docs/rules/

            } catch (e) {/**/}

Close

Disallow or enforce spaces inside of blocks after opening block and before closing block (block-spacing)

Rule Details

This rule enforces consistent spacing inside an open block token and the next token on the same line. This rule also enforces consistent spacing inside a close block token and previous token on the same line.

Options

This rule has a string option:

• "always" (default) requires one or more spaces
• "never" disallows spaces

always

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

/*eslint block-spacing: "error"*/

function foo() {return true;}
if (foo) { bar = 0;}
function baz() {let i = 0;
    return i;
}

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

/*eslint block-spacing: "error"*/

function foo() { return true; }
if (foo) { bar = 0; }

never

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

/*eslint block-spacing: ["error", "never"]*/

function foo() { return true; }
if (foo) { bar = 0;}

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

/*eslint block-spacing: ["error", "never"]*/

function foo() {return true;}
if (foo) {bar = 0;}

When Not To Use It

If you don't want to be notified about spacing style inside of blocks, you can safely disable this rule. Source: http://eslint.org/docs/rules/

    const {logger} = classInstance;

Close

Disallow Unused Variables (no-unused-vars)

Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

Rule Details

This rule is aimed at eliminating unused variables, functions, and parameters of functions.

A variable is considered to be used if any of the following are true:

• It represents a function that is called (doSomething())
• It is read (var y = x)
• It is passed into a function as an argument (doSomething(x))
• It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

A variable is not considered to be used if it is only ever assigned to (var x = 5) or declared.

Examples of incorrect code for this rule:

/*eslint no-unused-vars: "error"*/
/*global some_unused_var*/

// It checks variables you have defined as global
some_unused_var = 42;

var x;

// Write-only variables are not considered as used.
var y = 10;
y = 5;

// A read for a modification of itself is not considered as used.
var z = 0;
z = z + 1;

// By default, unused arguments cause warnings.
(function(foo) {
    return 5;
})();

// Unused recursive functions also cause warnings.
function fact(n) {
    if (n < 2) return 1;
    return n * fact(n - 1);
}

// When a function definition destructures an array, unused entries from the array also cause warnings.
function getY([x, y]) {
    return y;
}

Examples of correct code for this rule:

/*eslint no-unused-vars: "error"*/

var x = 10;
alert(x);

// foo is considered used here
myFunc(function foo() {
    // ...
}.bind(this));

(function(foo) {
    return foo;
})();

var myFunc;
myFunc = setTimeout(function() {
    // myFunc is considered used
    myFunc();
}, 50);

// Only the second argument from the descructured array is used.
function getY([, y]) {
    return y;
}

exported

In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

Note that /* exported */ has no effect for any of the following:

• when the environment is node or commonjs
• when parserOptions.sourceType is module
• when ecmaFeatures.globalReturn is true

The line comment // exported variableName will not work as exported is not line-specific.

Examples of correct code for /* exported variableName */ operation:

/* exported global_var */

var global_var = 42;

Options

This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

By default this rule is enabled with all option for variables and after-used for arguments.

{
    "rules": {
        "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
    }
}

vars

The vars option has two settings:

• all checks all variables for usage, including those in the global scope. This is the default setting.
• local checks only that locally-declared variables are used but will allow global variables to be unused.

vars: local

Examples of correct code for the { "vars": "local" } option:

/*eslint no-unused-vars: ["error", { "vars": "local" }]*/
/*global some_unused_var */

some_unused_var = 42;

varsIgnorePattern

The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

/*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/

var firstVarIgnored = 1;
var secondVar = 2;
console.log(secondVar);

args

The args option has three settings:

• after-used - only the last argument must be used. This allows you, for instance, to have two named parameters to a function and as long as you use the second argument, ESLint will not warn you about the first. This is the default setting.
• all - all named arguments must be used.
• none - do not check arguments.

args: after-used

Examples of incorrect code for the default { "args": "after-used" } option:

/*eslint no-unused-vars: ["error", { "args": "after-used" }]*/

// 1 error
// "baz" is defined but never used
(function(foo, bar, baz) {
    return bar;
})();

Examples of correct code for the default { "args": "after-used" } option:

/*eslint no-unused-vars: ["error", {"args": "after-used"}]*/

(function(foo, bar, baz) {
    return baz;
})();

args: all

Examples of incorrect code for the { "args": "all" } option:

/*eslint no-unused-vars: ["error", { "args": "all" }]*/

// 2 errors
// "foo" is defined but never used
// "baz" is defined but never used
(function(foo, bar, baz) {
    return bar;
})();

args: none

Examples of correct code for the { "args": "none" } option:

/*eslint no-unused-vars: ["error", { "args": "none" }]*/

(function(foo, bar, baz) {
    return bar;
})();

ignoreRestSiblings

The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

Examples of correct code for the { "ignoreRestSiblings": true } option:

/*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
// 'type' is ignored because it has a rest property sibling.
var { type, ...coords } = data;

argsIgnorePattern

The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

Examples of correct code for the { "argsIgnorePattern": "^_" } option:

/*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/

function foo(x, _y) {
    return x + 1;
}
foo();

caughtErrors

The caughtErrors option is used for catch block arguments validation.

It has two settings:

• none - do not check error objects. This is the default setting.
• all - all named arguments must be used.

caughtErrors: none

Not specifying this rule is equivalent of assigning it to none.

Examples of correct code for the { "caughtErrors": "none" } option:

/*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/

try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrors: all

Examples of incorrect code for the { "caughtErrors": "all" } option:

/*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/

// 1 error
// "err" is defined but never used
try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrorsIgnorePattern

The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

/*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/

try {
    //...
} catch (ignoreErr) {
    console.error("errors");
}

When Not To Use It

If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

    let devices = [];

Close

Suggest using const (prefer-const)

If a variable is never reassigned, using the const declaration is better.

const declaration tells readers, "this variable is never reassigned," reducing cognitive load and improving maintainability.

Rule Details

This rule is aimed at flagging variables that are declared using let keyword, but never reassigned after the initial assignment.

Examples of incorrect code for this rule:

/*eslint prefer-const: "error"*/
/*eslint-env es6*/

// it's initialized and never reassigned.
let a = 3;
console.log(a);

let a;
a = 0;
console.log(a);

// `i` is redefined (not reassigned) on each loop step.
for (let i in [1, 2, 3]) {
    console.log(i);
}

// `a` is redefined (not reassigned) on each loop step.
for (let a of [1, 2, 3]) {
    console.log(a);
}

Examples of correct code for this rule:

/*eslint prefer-const: "error"*/
/*eslint-env es6*/

// using const.
const a = 0;

// it's never initialized.
let a;
console.log(a);

// it's reassigned after initialized.
let a;
a = 0;
a = 1;
console.log(a);

// it's initialized in a different block from the declaration.
let a;
if (true) {
    a = 0;
}
console.log(a);

// it's initialized at a place that we cannot write a variable declaration.
let a;
if (true) a = 0;
console.log(a);

// `i` gets a new binding each iteration
for (const i in [1, 2, 3]) {
  console.log(i);
}

// `a` gets a new binding each iteration
for (const a of [1, 2, 3]) {
  console.log(a);
}

// `end` is never reassigned, but we cannot separate the declarations without modifying the scope.
for (let i = 0, end = 10; i < end; ++i) {
    console.log(a);
}

// suggest to use `no-var` rule.
var b = 3;
console.log(b);

Options

{
    "prefer-const": ["error", {
        "destructuring": "any",
        "ignoreReadBeforeAssign": false
    }]
}

destructuring

The kind of the way to address variables in destructuring. There are 2 values:

• "any" (default) - If any variables in destructuring should be const, this rule warns for those variables.
• "all" - If all variables in destructuring should be const, this rule warns the variables. Otherwise, ignores them.

Examples of incorrect code for the default {"destructuring": "any"} option:

/*eslint prefer-const: "error"*/
/*eslint-env es6*/

let {a, b} = obj;    /*error 'b' is never reassigned, use 'const' instead.*/
a = a + 1;

Examples of correct code for the default {"destructuring": "any"} option:

/*eslint prefer-const: "error"*/
/*eslint-env es6*/

// using const.
const {a: a0, b} = obj;
const a = a0 + 1;

// all variables are reassigned.
let {a, b} = obj;
a = a + 1;
b = b + 1;

Examples of incorrect code for the {"destructuring": "all"} option:

/*eslint prefer-const: ["error", {"destructuring": "all"}]*/
/*eslint-env es6*/

// all of `a` and `b` should be const, so those are warned.
let {a, b} = obj;    /*error 'a' is never reassigned, use 'const' instead.
                             'b' is never reassigned, use 'const' instead.*/

Examples of correct code for the {"destructuring": "all"} option:

/*eslint prefer-const: ["error", {"destructuring": "all"}]*/
/*eslint-env es6*/

// 'b' is never reassigned, but all of `a` and `b` should not be const, so those are ignored.
let {a, b} = obj;
a = a + 1;

ignoreReadBeforeAssign

This is an option to avoid conflicting with no-use-before-define rule (without "nofunc" option). If true is specified, this rule will ignore variables that are read between the declaration and the first assignment. Default is false.

Examples of correct code for the {"ignoreReadBeforeAssign": true} option:

/*eslint prefer-const: ["error", {"ignoreReadBeforeAssign": true}]*/
/*eslint-env es6*/

let timer;
function initialize() {
    if (foo()) {
        clearInterval(timer);
    }
}
timer = setInterval(initialize, 100);

Examples of correct code for the default {"ignoreReadBeforeAssign": false} option:

/*eslint prefer-const: ["error", {"ignoreReadBeforeAssign": false}]*/
/*eslint-env es6*/

const timer = setInterval(initialize, 100);
function initialize() {
    if (foo()) {
        clearInterval(timer);
    }
}

When Not To Use It

If you don't want to be notified about variables that are never reassigned after initial assignment, you can safely disable this rule.

Related Rules

• [no-var](no-var.md)
• [no-use-before-define](no-use-before-define.md) Source: http://eslint.org/docs/rules/

        await captureException(e, {extra:{networkingError: true}});

Close

enforce consistent spacing between keys and values in object literal properties (key-spacing)

This rule enforces spacing around the colon in object literal properties. It can verify each property individually, or it can ensure horizontal alignment of adjacent properties in an object literal.

Rule Details

This rule enforces consistent spacing between keys and values in object literal properties. In the case of long lines, it is acceptable to add a new line wherever whitespace is allowed.

Options

This rule has an object option:

• "beforeColon": false (default) | true
  • false: disallows spaces between the key and the colon in object literals.
  • true: requires at least one space between the key and the colon in object literals.
• "afterColon": true (default) | false
  • true: requires at least one space between the colon and the value in object literals.
  • false: disallows spaces between the colon and the value in object literals.
• "mode": "strict" (default) | "minimum"
  • "strict": enforces exactly one space before or after colons in object literals.
  • "minimum": enforces one or more spaces before or after colons in object literals.
• "align": "value" | "colon"
  • "value": enforces horizontal alignment of values in object literals.
  • "colon" enforces horizontal alignment of both colons and values in object literals.
• "align" with an object value allows for fine-grained spacing when values are being aligned in object literals.
• "singleLine" specifies a spacing style for single-line object literals.
• "multiLine" specifies a spacing style for multi-line object literals.

Please note that you can either use the top-level options or the grouped options (singleLine and multiLine) but not both.

beforeColon

Examples of incorrect code for this rule with the default { "beforeColon": false } option:

/*eslint key-spacing: ["error", { "beforeColon": false }]*/

var obj = { "foo" : 42 };

Examples of correct code for this rule with the default { "beforeColon": false } option:

/*eslint key-spacing: ["error", { "beforeColon": false }]*/

var obj = { "foo": 42 };

Examples of incorrect code for this rule with the { "beforeColon": true } option:

/*eslint key-spacing: ["error", { "beforeColon": true }]*/

var obj = { "foo": 42 };

Examples of correct code for this rule with the { "beforeColon": true } option:

/*eslint key-spacing: ["error", { "beforeColon": true }]*/

var obj = { "foo" : 42 };

afterColon

Examples of incorrect code for this rule with the default { "afterColon": true } option:

/*eslint key-spacing: ["error", { "afterColon": true }]*/

var obj = { "foo":42 };

Examples of correct code for this rule with the default { "afterColon": true } option:

/*eslint key-spacing: ["error", { "afterColon": true }]*/

var obj = { "foo": 42 };

Examples of incorrect code for this rule with the { "afterColon": false } option:

/*eslint key-spacing: ["error", { "afterColon": false }]*/

var obj = { "foo": 42 };

Examples of correct code for this rule with the { "afterColon": false } option:

/*eslint key-spacing: ["error", { "afterColon": false }]*/

var obj = { "foo":42 };

mode

Examples of incorrect code for this rule with the default { "mode": "strict" } option:

/*eslint key-spacing: ["error", { "mode": "strict" }]*/

call({
    foobar: 42,
    bat:    2 * 2
});

Examples of correct code for this rule with the default { "mode": "strict" } option:

/*eslint key-spacing: ["error", { "mode": "strict" }]*/

call({
    foobar: 42,
    bat: 2 * 2
});

Examples of correct code for this rule with the { "mode": "minimum" } option:

/*eslint key-spacing: ["error", { "mode": "minimum" }]*/

call({
    foobar: 42,
    bat:    2 * 2
});

align

Examples of incorrect code for this rule with the { "align": "value" } option:

/*eslint key-spacing: ["error", { "align": "value" }]*/

var obj = {
    a: value,
    bcde:  42,
    fg :   foo()
};

Examples of correct code for this rule with the { "align": "value" } option:

/*eslint key-spacing: ["error", { "align": "value" }]*/

var obj = {
    a:    value,
    bcde: 42,

    fg: foo(),
    h:  function() {
        return this.a;
    },
    ijkl: 'Non-consecutive lines form a new group'
};

var obj = { a: "foo", longPropertyName: "bar" };

Examples of incorrect code for this rule with the { "align": "colon" } option:

/*eslint key-spacing: ["error", { "align": "colon" }]*/

call({
    foobar: 42,
    bat:    2 * 2
});

Examples of correct code for this rule with the { "align": "colon" } option:

/*eslint key-spacing: ["error", { "align": "colon" }]*/

call({
    foobar: 42,
    bat   : 2 * 2
});

align

The align option can take additional configuration through the beforeColon, afterColon, mode, and on options.

If align is defined as an object, but not all of the parameters are provided, undefined parameters will default to the following:

// Defaults
align: {
    "beforeColon": false,
    "afterColon": true,
    "on": "colon",
    "mode": "strict"
}

Examples of correct code for this rule with sample { "align": { } } options:

/*eslint key-spacing: ["error", {
    "align": {
        "beforeColon": true,
        "afterColon": true,
        "on": "colon"
    }
}]*/

var obj = {
    "one"   : 1,
    "seven" : 7
}

/*eslint key-spacing: ["error", {
    "align": {
        "beforeColon": false,
        "afterColon": false,
        "on": "value"
    }
}]*/

var obj = {
    "one":  1,
    "seven":7
}

align and multiLine

The multiLine and align options can differ, which allows for fine-tuned control over the key-spacing of your files. align will not inherit from multiLine if align is configured as an object.

multiLine is used any time an object literal spans multiple lines. The align configuration is used when there is a group of properties in the same object. For example:

var myObj = {
  key1: 1, // uses multiLine

  key2: 2, // uses align (when defined)
  key3: 3, // uses align (when defined)

  key4: 4 // uses multiLine
}

Examples of incorrect code for this rule with sample { "align": { }, "multiLine": { } } options:

/*eslint key-spacing: ["error", {
    "multiLine": {
        "beforeColon": false,
        "afterColon":true
    },
    "align": {
        "beforeColon": true,
        "afterColon": true,
        "on": "colon"
    }
}]*/

var obj = {
    "myObjectFunction": function() {
        // Do something
    },
    "one"             : 1,
    "seven"           : 7
}

Examples of correct code for this rule with sample { "align": { }, "multiLine": { } } options:

/*eslint key-spacing: ["error", {
    "multiLine": {
        "beforeColon": false,
        "afterColon": true

    },
    "align": {
        "beforeColon": true,
        "afterColon": true,
        "on": "colon"
    }
}]*/

var obj = {
    "myObjectFunction": function() {
        // Do something
        //
    }, // These are two separate groups, so no alignment between `myObjectFuction` and `one`
    "one"   : 1,
    "seven" : 7 // `one` and `seven` are in their own group, and therefore aligned
}

singleLine and multiLine

Examples of correct code for this rule with sample { "singleLine": { }, "multiLine": { } } options:

/*eslint "key-spacing": [2, {
    "singleLine": {
        "beforeColon": false,
        "afterColon": true
    },
    "multiLine": {
        "beforeColon": true,
        "afterColon": true,
        "align": "colon"
    }
}]*/
var obj = { one: 1, "two": 2, three: 3 };
var obj2 = {
    "two" : 2,
    three : 3
};

When Not To Use It

If you have another convention for property spacing that might not be consistent with the available options, or if you want to permit multiple styles concurrently you can safely disable this rule. Source: http://eslint.org/docs/rules/

    NON_EMPTY_STRING_OR_NUll: Symbol('nonEmptyStringOrNull'),

Close

Require CamelCase (camelcase)

When it comes to naming variables, style guides generally fall into one of two camps: camelcase (variableName) and underscores (variable_name). This rule focuses on using the camelcase approach. If your style guide calls for camelCasing your variable names, then this rule is for you!

Rule Details

This rule looks for any underscores (_) located within the source code. It ignores leading and trailing underscores and only checks those in the middle of a variable name. If ESLint decides that the variable is a constant (all uppercase), then no warning will be thrown. Otherwise, a warning will be thrown. This rule only flags definitions and assignments but not function calls. In case of ES6 import statements, this rule only targets the name of the variable that will be imported into the local module scope.

Options

This rule has an object option:

• "properties": "always" (default) enforces camelcase style for property names
• "properties": "never" does not check property names

always

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

/*eslint camelcase: "error"*/

import { no_camelcased } from "external-module"

var my_favorite_color = "#112C85";

function do_something() {
    // ...
}

obj.do_something = function() {
    // ...
};

function foo({ no_camelcased }) {
    // ...
};

function foo({ isCamelcased: no_camelcased }) {
    // ...
}

function foo({ no_camelcased = 'default value' }) {
    // ...
};

var obj = {
    my_pref: 1
};

var { category_id = 1 } = query;

var { foo: no_camelcased } = bar;

var { foo: bar_baz = 1 } = quz;

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

/*eslint camelcase: "error"*/

import { no_camelcased as camelCased } from "external-module";

var myFavoriteColor   = "#112C85";
var _myFavoriteColor  = "#112C85";
var myFavoriteColor_  = "#112C85";
var MY_FAVORITE_COLOR = "#112C85";
var foo = bar.baz_boom;
var foo = { qux: bar.baz_boom };

obj.do_something();
do_something();
new do_something();

var { category_id: category } = query;

function foo({ isCamelCased }) {
    // ...
};

function foo({ isCamelCased: isAlsoCamelCased }) {
    // ...
}

function foo({ isCamelCased = 'default value' }) {
    // ...
};

var { categoryId = 1 } = query;

var { foo: isCamelCased } = bar;

var { foo: isCamelCased = 1 } = quz;

never

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

/*eslint camelcase: ["error", {properties: "never"}]*/

var obj = {
    my_pref: 1
};

When Not To Use It

If you have established coding standards using a different naming convention (separating words with underscores), turn this rule off. Source: http://eslint.org/docs/rules/

            } catch (e) {/**/}

Close

Disallow or enforce spaces inside of blocks after opening block and before closing block (block-spacing)

Rule Details

This rule enforces consistent spacing inside an open block token and the next token on the same line. This rule also enforces consistent spacing inside a close block token and previous token on the same line.

Options

This rule has a string option:

• "always" (default) requires one or more spaces
• "never" disallows spaces

always

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

/*eslint block-spacing: "error"*/

function foo() {return true;}
if (foo) { bar = 0;}
function baz() {let i = 0;
    return i;
}

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

/*eslint block-spacing: "error"*/

function foo() { return true; }
if (foo) { bar = 0; }

never

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

/*eslint block-spacing: ["error", "never"]*/

function foo() { return true; }
if (foo) { bar = 0;}

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

/*eslint block-spacing: ["error", "never"]*/

function foo() {return true;}
if (foo) {bar = 0;}

When Not To Use It

If you don't want to be notified about spacing style inside of blocks, you can safely disable this rule. Source: http://eslint.org/docs/rules/