Showing 16 of 16 total issues
Similar blocks of code found in 4 locations. Consider refactoring. Open
edit (resource, params) {
this._validateIdPresence(params)
const path = `${snakeCase(resource)}/:id/edit`
return this._buildPath('get', path, params)
- Read upRead up
Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 58.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76
Similar blocks of code found in 4 locations. Consider refactoring. Open
update (resource, params) {
this._validateIdPresence(params)
const path = `${snakeCase(resource)}/:id`
return this._buildPath('patch', path, params)
- Read upRead up
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 58.
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
Similar blocks of code found in 4 locations. Consider refactoring. Open
show (resource, params) {
this._validateIdPresence(params)
const path = `${snakeCase(resource)}/:id`
return this._buildPath('get', path, params)
- Read upRead up
Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 58.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76
Similar blocks of code found in 4 locations. Consider refactoring. Open
destroy (resource, params) {
this._validateIdPresence(params)
const path = `${snakeCase(resource)}/:id`
return this._buildPath('delete', path, params)
- Read upRead up
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 58.
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
Similar blocks of code found in 3 locations. Consider refactoring. Open
post (path, params = {}) {
const requestInfo = this._injectPathParams(path, params, { skipQuery: true })
return merge(requestInfo, { method: 'post' })
}
- Read upRead up
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 52.
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
Similar blocks of code found in 3 locations. Consider refactoring. Open
put (path, params = {}) {
const requestInfo = this._injectPathParams(path, params, { skipQuery: true })
return merge(requestInfo, { method: 'put' })
}
- Read upRead up
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 52.
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
Similar blocks of code found in 3 locations. Consider refactoring. Open
patch (path, params = {}) {
const requestInfo = this._injectPathParams(path, params, { skipQuery: true })
return merge(requestInfo, { method: 'patch' })
}
- Read upRead up
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 52.
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
Use path.join() or path.resolve() instead of + to create paths. Open
path: __dirname + '/dist',
- Read upRead up
- Exclude checks
Disallow string concatenation when using __dirname
and __filename
(no-path-concat)
In Node.js, the __dirname
and __filename
global variables contain the directory path and the file path of the currently executing script file, respectively. Sometimes, developers try to use these variables to create paths to other files, such as:
var fullPath = __dirname + "/foo.js";
However, there are a few problems with this. First, you can't be sure what type of system the script is running on. Node.js can be run on any computer, including Windows, which uses a different path separator. It's very easy, therefore, to create an invalid path using string concatenation and assuming Unix-style separators. There's also the possibility of having double separators, or otherwise ending up with an invalid path.
In order to avoid any confusion as to how to create the correct path, Node.js provides the path
module. This module uses system-specific information to always return the correct value. So you can rewrite the previous example as:
var fullPath = path.join(__dirname, "foo.js");
This example doesn't need to include separators as path.join()
will do it in the most appropriate manner. Alternately, you can use path.resolve()
to retrieve the fully-qualified path:
var fullPath = path.resolve(__dirname, "foo.js");
Both path.join()
and path.resolve()
are suitable replacements for string concatenation wherever file or directory paths are being created.
Rule Details
This rule aims to prevent string concatenation of directory paths in Node.js
Examples of incorrect code for this rule:
/*eslint no-path-concat: "error"*/
var fullPath = __dirname + "/foo.js";
var fullPath = __filename + "/foo.js";
Examples of correct code for this rule:
/*eslint no-path-concat: "error"*/
var fullPath = dirname + "/foo.js";
When Not To Use It
If you want to allow string concatenation of path names. Source: http://eslint.org/docs/rules/
Missing space before function parentheses. Open
constructor(parameter) {
- Read upRead up
- Exclude checks
Require or disallow a space before function parenthesis (space-before-function-paren)
When formatting a function, whitespace is allowed between the function name or function
keyword and the opening paren. Named functions also require a space between the function
keyword and the function name, but anonymous functions require no whitespace. For example:
function withoutSpace(x) {
// ...
}
function withSpace (x) {
// ...
}
var anonymousWithoutSpace = function() {};
var anonymousWithSpace = function () {};
Style guides may require a space after the function
keyword for anonymous functions, while others specify no whitespace. Similarly, the space after a function name may or may not be required.
Rule Details
This rule aims to enforce consistent spacing before function parentheses and as such, will warn whenever whitespace doesn't match the preferences specified.
Options
This rule has a string option or an object option:
{
"space-before-function-paren": ["error", "always"],
// or
"space-before-function-paren": ["error", {
"anonymous": "always",
"named": "always",
"asyncArrow": "ignore"
}],
}
-
always
(default) requires a space followed by the(
of arguments. -
never
disallows any space followed by the(
of arguments.
The string option does not check async arrow function expressions for backward compatibility.
You can also use a separate option for each type of function.
Each of the following options can be set to "always"
, "never"
, or "ignore"
.
Default is "always"
basically.
-
anonymous
is for anonymous function expressions (e.g.function () {}
). -
named
is for named function expressions (e.g.function foo () {}
). -
asyncArrow
is for async arrow function expressions (e.g.async () => {}
).asyncArrow
is set to"ignore"
by default for backwards compatibility.
"always"
Examples of incorrect code for this rule with the default "always"
option:
/*eslint space-before-function-paren: "error"*/
/*eslint-env es6*/
function foo() {
// ...
}
var bar = function() {
// ...
};
var bar = function foo() {
// ...
};
class Foo {
constructor() {
// ...
}
}
var foo = {
bar() {
// ...
}
};
Examples of correct code for this rule with the default "always"
option:
/*eslint space-before-function-paren: "error"*/
/*eslint-env es6*/
function foo () {
// ...
}
var bar = function () {
// ...
};
var bar = function foo () {
// ...
};
class Foo {
constructor () {
// ...
}
}
var foo = {
bar () {
// ...
}
};
// async arrow function expressions are ignored by default.
var foo = async () => 1
var foo = async() => 1
"never"
Examples of incorrect code for this rule with the "never"
option:
/*eslint space-before-function-paren: ["error", "never"]*/
/*eslint-env es6*/
function foo () {
// ...
}
var bar = function () {
// ...
};
var bar = function foo () {
// ...
};
class Foo {
constructor () {
// ...
}
}
var foo = {
bar () {
// ...
}
};
Examples of correct code for this rule with the "never"
option:
/*eslint space-before-function-paren: ["error", "never"]*/
/*eslint-env es6*/
function foo() {
// ...
}
var bar = function() {
// ...
};
var bar = function foo() {
// ...
};
class Foo {
constructor() {
// ...
}
}
var foo = {
bar() {
// ...
}
};
// async arrow function expressions are ignored by default.
var foo = async () => 1
var foo = async() => 1
{"anonymous": "always", "named": "never", "asyncArrow": "always"}
Examples of incorrect code for this rule with the {"anonymous": "always", "named": "never", "asyncArrow": "always"}
option:
/*eslint space-before-function-paren: ["error", {"anonymous": "always", "named": "never", "asyncArrow": "always"}]*/
/*eslint-env es6*/
function foo () {
// ...
}
var bar = function() {
// ...
};
class Foo {
constructor () {
// ...
}
}
var foo = {
bar () {
// ...
}
};
var foo = async(a) => await a
Examples of correct code for this rule with the {"anonymous": "always", "named": "never", "asyncArrow": "always"}
option:
/*eslint space-before-function-paren: ["error", {"anonymous": "always", "named": "never", "asyncArrow": "always"}]*/
/*eslint-env es6*/
function foo() {
// ...
}
var bar = function () {
// ...
};
class Foo {
constructor() {
// ...
}
}
var foo = {
bar() {
// ...
}
};
var foo = async (a) => await a
{"anonymous": "never", "named": "always"}
Examples of incorrect code for this rule with the {"anonymous": "never", "named": "always"}
option:
/*eslint space-before-function-paren: ["error", { "anonymous": "never", "named": "always" }]*/
/*eslint-env es6*/
function foo() {
// ...
}
var bar = function () {
// ...
};
class Foo {
constructor() {
// ...
}
}
var foo = {
bar() {
// ...
}
};
Examples of correct code for this rule with the {"anonymous": "never", "named": "always"}
option:
/*eslint space-before-function-paren: ["error", { "anonymous": "never", "named": "always" }]*/
/*eslint-env es6*/
function foo () {
// ...
}
var bar = function() {
// ...
};
class Foo {
constructor () {
// ...
}
}
var foo = {
bar () {
// ...
}
};
{"anonymous": "ignore", "named": "always"}
Examples of incorrect code for this rule with the {"anonymous": "ignore", "named": "always"}
option:
/*eslint space-before-function-paren: ["error", { "anonymous": "ignore", "named": "always" }]*/
/*eslint-env es6*/
function foo() {
// ...
}
class Foo {
constructor() {
// ...
}
}
var foo = {
bar() {
// ...
}
};
Examples of correct code for this rule with the {"anonymous": "ignore", "named": "always"}
option:
/*eslint space-before-function-paren: ["error", { "anonymous": "ignore", "named": "always" }]*/
/*eslint-env es6*/
var bar = function() {
// ...
};
var bar = function () {
// ...
};
function foo () {
// ...
}
class Foo {
constructor () {
// ...
}
}
var foo = {
bar () {
// ...
}
};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing before function parenthesis.
Related Rules
- [space-after-keywords](space-after-keywords.md)
- [space-return-throw-case](space-return-throw-case.md) Source: http://eslint.org/docs/rules/
Unexpected trailing comma. Open
minimize: true,
- Read upRead up
- Exclude checks
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/
Extra semicolon. Open
var webpack = require('webpack');
- Read upRead up
- Exclude checks
require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who says that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option:
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Extra semicolon. Open
module.exports = config;
- Read upRead up
- Exclude checks
require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who says that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option:
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Use path.join() or path.resolve() instead of + to create paths. Open
context: __dirname + '/src',
- Read upRead up
- Exclude checks
Disallow string concatenation when using __dirname
and __filename
(no-path-concat)
In Node.js, the __dirname
and __filename
global variables contain the directory path and the file path of the currently executing script file, respectively. Sometimes, developers try to use these variables to create paths to other files, such as:
var fullPath = __dirname + "/foo.js";
However, there are a few problems with this. First, you can't be sure what type of system the script is running on. Node.js can be run on any computer, including Windows, which uses a different path separator. It's very easy, therefore, to create an invalid path using string concatenation and assuming Unix-style separators. There's also the possibility of having double separators, or otherwise ending up with an invalid path.
In order to avoid any confusion as to how to create the correct path, Node.js provides the path
module. This module uses system-specific information to always return the correct value. So you can rewrite the previous example as:
var fullPath = path.join(__dirname, "foo.js");
This example doesn't need to include separators as path.join()
will do it in the most appropriate manner. Alternately, you can use path.resolve()
to retrieve the fully-qualified path:
var fullPath = path.resolve(__dirname, "foo.js");
Both path.join()
and path.resolve()
are suitable replacements for string concatenation wherever file or directory paths are being created.
Rule Details
This rule aims to prevent string concatenation of directory paths in Node.js
Examples of incorrect code for this rule:
/*eslint no-path-concat: "error"*/
var fullPath = __dirname + "/foo.js";
var fullPath = __filename + "/foo.js";
Examples of correct code for this rule:
/*eslint no-path-concat: "error"*/
var fullPath = dirname + "/foo.js";
When Not To Use It
If you want to allow string concatenation of path names. Source: http://eslint.org/docs/rules/
Extra semicolon. Open
module.exports = require('./dist/rails-ranger.min.js');
- Read upRead up
- Exclude checks
require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who says that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option:
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
'webpack' is assigned a value but never used. Open
var webpack = require('webpack');
- Read upRead up
- Exclude checks
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
orcommonjs
- when
parserOptions.sourceType
ismodule
- when
ecmaFeatures.globalReturn
istrue
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/
Extra semicolon. Open
module.exports = require('./dist/rails-ranger.js');
- Read upRead up
- Exclude checks
require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who says that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option:
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/