Airbnb JavaScript Style Guide() { (Edited by / for Zoro)

A mostly reasonable approach to JavaScript

Note: this guide assumes you are using Babel, and requires that you use babel-preset-airbnb or the equivalent. It also assumes you are installing shims/polyfills in your app, with airbnb-browser-shims or the equivalent.

Other Style Guides

• ES5 (Deprecated)
• React
• CSS-in-JavaScript
• CSS & Sass
• Ruby

ZORO exceptions

Within this document a number of exceptions and notes have been added to indicate how ZORO intends to extend Airbnb's style guide.

@ZORO NOTE contains information regarding its implementation or the rule was eventually agreed upon after discussion. These will not require changes to airbnb style guide lint configuration.

@ZORO EXCEPTION indicates a rule that was fundamentally disagreed with or is not possible to implement due to architectural limitations. These may require changes to airbnb style guide lint configuration.

The following is a short list of these notes and exceptions:

Notes

Note: (✓) indicates agreed upon.

• 3.8 Objects - Rest Spread ✓
• 5.3 Destructuring - Object over array ✓
• 6.1 Strings - Quotes ✓
• 9.1 Constructors - Use Class ✓
• 10.3 Modules - No Export from Import
• 15.7 Comparison - Unneeded ternary ✓
• 15.8 Comparison - No mixed operators
• 19.6 Whitespace - Chains
• 19.7 Whitespace - After blocks ✓
• 19.8 Whitespace - Padded blocks ✓
• 20.1 Commas - Leading trailing ✓
• 25.1 Events - Hash ✓

Exceptions

• 4.4 Objects - Array.from
• 7.1 Functions - Declarations
• 7.2 Functions - IIFE
• 7.11 Functions - Signature Spacing
• 7.12 Functions - Mutate Params
• 8.1 Arrows - Using them
• 8.4 Arrows - One argument parentheses
• 10.2 Modules - No Wildcard
• 10.8 Module - Multiline imports
• 10.9 Module - No webpack loader syntax
• 13.6 Variables - Unary inc / dec
• 18.2 Comments - Single line
• 18.4 - 18.6 Comments - Action items
• 19.11 Whitespace - In braces
• 19.12 Whitespace - Max Length
• 23.1 Naming - Descriptive
• 23.5 Naming - Self / this
• 23.9 Naming - Acronyms / initialisms
• 24.2 Accessors - Getters Setters
• 24.4 Accessors - Consistent
• 26.1 jQuery - Dollar Prefix

Table of Contents

1. Types
2. References
3. Objects
4. Arrays
5. Destructuring
6. Strings
7. Functions
8. Arrow Functions
9. Classes & Constructors
10. Modules
11. Iterators and Generators
12. Properties
13. Variables
14. Hoisting
15. Comparison Operators & Equality
16. Blocks
17. Control Statements
18. Comments
19. Whitespace
20. Commas
21. Semicolons
22. Type Casting & Coercion
23. Naming Conventions
24. Accessors
25. Events
26. jQuery
27. ECMAScript 5 Compatibility
28. ECMAScript 6+ (ES 2015+) Styles
29. Standard Library
30. Testing
31. Performance
32. Resources
33. In the Wild
34. Translation
35. The JavaScript Style Guide Guide
36. Chat With Us About JavaScript
37. Contributors
38. License
39. Amendments

Types

• 1.1 Primitives: When you access a primitive type you work directly on its value.

  • string
  • number
  • boolean
  • null
  • undefined
  • symbol

  const foo = 1;
  let bar = foo;
  
  bar = 9;
  
  console.log(foo, bar); // => 1, 9

  • Symbols cannot be faithfully polyfilled, so they should not be used when targeting browsers/environments that don't support them natively.

• 1.2 Complex: When you access a complex type you work on a reference to its value.

  • object
  • array
  • function

  const foo = [1, 2];
  const bar = foo;
  
  bar[0] = 9;
  
  console.log(foo[0], bar[0]); // => 9, 9

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References

• 2.1 Use const for all of your references; avoid using var. eslint: prefer-const, no-const-assign

  Why? This ensures that you can’t reassign your references, which can lead to bugs and difficult to comprehend code.

  // bad
  var a = 1;
  var b = 2;
  
  // good
  const a = 1;
  const b = 2;

• 2.2 If you must reassign references, use let instead of var. eslint: no-var jscs: disallowVar

  Why? let is block-scoped rather than function-scoped like var.

  // bad
  var count = 1;
  if (true) {
    count += 1;
  }
  
  // good, use the let.
  let count = 1;
  if (true) {
    count += 1;
  }

• 2.3 Note that both let and const are block-scoped.

  // const and let only exist in the blocks they are defined in.
  {
    let a = 1;
    const b = 1;
  }
  console.log(a); // ReferenceError
  console.log(b); // ReferenceError

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Objects

• 3.1 Use the literal syntax for object creation. eslint: no-new-object

  // bad
  const item = new Object();
  
  // good
  const item = {};

• 3.2 Use computed property names when creating objects with dynamic property names.

  Why? They allow you to define all the properties of an object in one place.

  function getKey(k) {
    return `a key named ${k}`;
  }
  
  // bad
  const obj = {
    id: 5,
    name: 'San Francisco',
  };
  obj[getKey('enabled')] = true;
  
  // good
  const obj = {
    id: 5,
    name: 'San Francisco',
    [getKey('enabled')]: true,
  };

• 3.3 Use object method shorthand. eslint: object-shorthand jscs: requireEnhancedObjectLiterals

  // bad
  const atom = {
    value: 1,
  
    addValue: function (value) {
      return atom.value + value;
    },
  };
  
  // good
  const atom = {
    value: 1,
  
    addValue(value) {
      return atom.value + value;
    },
  };

• 3.4 Use property value shorthand. eslint: object-shorthand jscs: requireEnhancedObjectLiterals

  Why? It is shorter to write and descriptive.

  const lukeSkywalker = 'Luke Skywalker';
  
  // bad
  const obj = {
    lukeSkywalker: lukeSkywalker,
  };
  
  // good
  const obj = {
    lukeSkywalker,
  };

• 3.5 Group your shorthand properties at the beginning of your object declaration.

  Why? It’s easier to tell which properties are using the shorthand.

  const anakinSkywalker = 'Anakin Skywalker';
  const lukeSkywalker = 'Luke Skywalker';
  
  // bad
  const obj = {
    episodeOne: 1,
    twoJediWalkIntoACantina: 2,
    lukeSkywalker,
    episodeThree: 3,
    mayTheFourth: 4,
    anakinSkywalker,
  };
  
  // good
  const obj = {
    lukeSkywalker,
    anakinSkywalker,
    episodeOne: 1,
    twoJediWalkIntoACantina: 2,
    episodeThree: 3,
    mayTheFourth: 4,
  };

• 3.6 Only quote properties that are invalid identifiers. eslint: quote-props jscs: disallowQuotedKeysInObjects

  Why? In general we consider it subjectively easier to read. It improves syntax highlighting, and is also more easily optimized by many JS engines.

  // bad
  const bad = {
    'foo': 3,
    'bar': 4,
    'data-blah': 5,
  };
  
  // good
  const good = {
    foo: 3,
    bar: 4,
    'data-blah': 5,
  };

• 3.7 Do not call Object.prototype methods directly, such as hasOwnProperty, propertyIsEnumerable, and isPrototypeOf.

  Why? These methods may be shadowed by properties on the object in question - consider { hasOwnProperty: false } - or, the object may be a null object (Object.create(null)).

  // bad
  console.log(object.hasOwnProperty(key));
  
  // good
  console.log(Object.prototype.hasOwnProperty.call(object, key));
  
  // best
  const has = Object.prototype.hasOwnProperty; // cache the lookup once, in module scope.
  /* or */
  import has from 'has'; // https://www.npmjs.com/package/has
  // ...
  console.log(has.call(object, key));

• 3.8 Prefer the object spread operator over Object.assign to shallow-copy objects. Use the object rest operator to get a new object with certain properties omitted.

@ZORO NOTE: This has been agreed upon.

```javascript
// very bad
const original = { a: 1, b: 2 };
const copy = Object.assign(original, { c: 3 }); // this mutates `original` ಠ_ಠ
delete copy.a; // so does this

// bad
const original = { a: 1, b: 2 };
const copy = Object.assign({}, original, { c: 3 }); // copy => { a: 1, b: 2, c: 3 }

// good
const original = { a: 1, b: 2 };
const copy = { ...original, c: 3 }; // copy => { a: 1, b: 2, c: 3 }

const { a, ...noA } = copy; // noA => { b: 2, c: 3 }
```

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Arrays

• 4.1 Use the literal syntax for array creation. eslint: no-array-constructor

  // bad
  const items = new Array();
  
  // good
  const items = [];

• 4.2 Use Array#push instead of direct assignment to add items to an array.

  const someStack = [];
  
  // bad
  someStack[someStack.length] = 'abracadabra';
  
  // good
  someStack.push('abracadabra');

• 4.3 Use array spreads ... to copy arrays.

  // bad
  const len = items.length;
  const itemsCopy = [];
  let i;
  
  for (i = 0; i < len; i += 1) {
    itemsCopy[i] = items[i];
  }
  
  // good
  const itemsCopy = [...items];

• 4.4 To convert an array-like object to an array, use spreads ... instead of Array.from.

@ZORO EXCEPTION: ignore because 4.5

```javascript
const foo = document.querySelectorAll('.foo');

// good
const nodes = Array.from(foo);

// best
const nodes = [...foo];
```

• 4.5 Use Array.from instead of spread ... for mapping over iterables, because it avoids creating an intermediate array.

  // bad
  const baz = [...foo].map(bar);
  
  // good
  const baz = Array.from(foo, bar);

• 4.6 Use return statements in array method callbacks. It’s ok to omit the return if the function body consists of a single statement returning an expression without side effects, following 8.2. eslint: array-callback-return

  // good
  [1, 2, 3].map((x) => {
    const y = x + 1;
    return x * y;
  });
  
  // good
  [1, 2, 3].map(x => x + 1);
  
  // bad - no returned value means `memo` becomes undefined after the first iteration
  [[0, 1], [2, 3], [4, 5]].reduce((memo, item, index) => {
    const flatten = memo.concat(item);
    memo[index] = flatten;
  });
  
  // good
  [[0, 1], [2, 3], [4, 5]].reduce((memo, item, index) => {
    const flatten = memo.concat(item);
    memo[index] = flatten;
    return flatten;
  });
  
  // bad
  inbox.filter((msg) => {
    const { subject, author } = msg;
    if (subject === 'Mockingbird') {
      return author === 'Harper Lee';
    } else {
      return false;
    }
  });
  
  // good
  inbox.filter((msg) => {
    const { subject, author } = msg;
    if (subject === 'Mockingbird') {
      return author === 'Harper Lee';
    }
  
    return false;
  });

• 4.7 Use line breaks after open and before close array brackets if an array has multiple lines

// bad
const arr = [
  [0, 1], [2, 3], [4, 5],
];

const objectInArray = [{
  id: 1,
}, {
  id: 2,
}];

const numberInArray = [
  1, 2,
];

// good
const arr = [[0, 1], [2, 3], [4, 5]];

const objectInArray = [
  {
    id: 1,
  },
  {
    id: 2,
  },
];

const numberInArray = [
  1,
  2,
];

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Destructuring

• 5.1 Use object destructuring when accessing and using multiple properties of an object. eslint: prefer-destructuring jscs: requireObjectDestructuring

  Why? Destructuring saves you from creating temporary references for those properties.

  // bad
  function getFullName(user) {
    const firstName = user.firstName;
    const lastName = user.lastName;
  
    return `${firstName} ${lastName}`;
  }
  
  // good
  function getFullName(user) {
    const { firstName, lastName } = user;
    return `${firstName} ${lastName}`;
  }
  
  // best
  function getFullName({ firstName, lastName }) {
    return `${firstName} ${lastName}`;
  }

• 5.2 Use array destructuring. eslint: prefer-destructuring jscs: requireArrayDestructuring

  const arr = [1, 2, 3, 4];
  
  // bad
  const first = arr[0];
  const second = arr[1];
  
  // good
  const [first, second] = arr;

• 5.3 Use object destructuring for multiple return values, not array destructuring. jscs: disallowArrayDestructuringReturn

@ZORO NOTE: This has been agreed on.

> Why? You can add new properties over time or change the order of things without breaking call sites.

```javascript
// bad
function processInput(input) {
  // then a miracle occurs
  return [left, right, top, bottom];
}

// the caller needs to think about the order of return data
const [left, __, top] = processInput(input);

// good
function processInput(input) {
  // then a miracle occurs
  return { left, right, top, bottom };
}

// the caller selects only the data they need
const { left, top } = processInput(input);
```

⬆ back to top

Strings

• 6.1 Use single quotes '' for strings. eslint: quotes jscs: validateQuoteMarks

@ZORO NOTE: This has been agreed on.

```javascript
// bad
const name = "Capt. Janeway";

// bad - template literals should contain interpolation or newlines
const name = `Capt. Janeway`;

// good
const name = 'Capt. Janeway';
```

• 6.2 Strings that cause the line to go over 100 characters should not be written across multiple lines using string concatenation.

  Why? Broken strings are painful to work with and make code less searchable.

  // bad
  const errorMessage = 'This is a super long error that was thrown because \
  of Batman. When you stop to think about how Batman had anything to do \
  with this, you would get nowhere \
  fast.';
  
  // bad
  const errorMessage = 'This is a super long error that was thrown because ' +
    'of Batman. When you stop to think about how Batman had anything to do ' +
    'with this, you would get nowhere fast.';
  
  // good
  const errorMessage = 'This is a super long error that was thrown because of Batman. When you stop to think about how Batman had anything to do with this, you would get nowhere fast.';

• 6.3 When programmatically building up strings, use template strings instead of concatenation. eslint: prefer-template template-curly-spacing jscs: requireTemplateStrings

  Why? Template strings give you a readable, concise syntax with proper newlines and string interpolation features.

  // bad
  function sayHi(name) {
    return 'How are you, ' + name + '?';
  }
  
  // bad
  function sayHi(name) {
    return ['How are you, ', name, '?'].join();
  }
  
  // bad
  function sayHi(name) {
    return `How are you, ${ name }?`;
  }
  
  // good
  function sayHi(name) {
    return `How are you, ${name}?`;
  }

• 6.4 Never use eval() on a string, it opens too many vulnerabilities. eslint: no-eval

• 6.5 Do not unnecessarily escape characters in strings. eslint: no-useless-escape

  Why? Backslashes harm readability, thus they should only be present when necessary.

  // bad
  const foo = '\'this\' \i\s \"quoted\"';
  
  // good
  const foo = '\'this\' is "quoted"';
  const foo = `my name is '${name}'`;

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Functions

• 7.1 Use named function expressions instead of function declarations. eslint: func-style jscs: disallowFunctionDeclarations

@ZORO EXCEPTIONß: Ignore this rule for now, maybe implemented as a requirement in the future.

> Why? Function declarations are hoisted, which means that it’s easy - too easy - to reference the function before it is defined in the file. This harms readability and maintainability. If you find that a function’s definition is large or complex enough that it is interfering with understanding the rest of the file, then perhaps it’s time to extract it to its own module! Don’t forget to explicitly name the expression, regardless of whether or not the name is inferred from the containing variable (which is often the case in modern browsers or when using compilers such as Babel). This eliminates any assumptions made about the Error's call stack. ([Discussion](https://github.com/airbnb/javascript/issues/794))

```javascript
// bad
function foo() {
  // ...
}

// bad
const foo = function () {
  // ...
};

// good
// lexical name distinguished from the variable-referenced invocation(s)
const short = function longUniqueMoreDescriptiveLexicalFoo() {
  // ...
};
```

• 7.2 Wrap immediately invoked function expressions in parentheses. eslint: wrap-iife jscs: requireParenthesesAroundIIFE

@ZORO EXCEPTION: Ignore, keep current specification which dictates the function rather than the invocation is wrapped in parentheses

> Why? An immediately invoked function expression is a single unit - wrapping both it, and its invocation parens, in parens, cleanly expresses this. Note that in a world with modules everywhere, you almost never need an IIFE.

```javascript
// immediately-invoked function expression (IIFE)
(function () {
  console.log('Welcome to the Internet. Please follow me.');
}());
```

• 7.3 Never declare a function in a non-function block (if, while, etc). Assign the function to a variable instead. Browsers will allow you to do it, but they all interpret it differently, which is bad news bears. eslint: no-loop-func

• 7.4 Note: ECMA-262 defines a block as a list of statements. A function declaration is not a statement.

  // bad
  if (currentUser) {
    function test() {
      console.log('Nope.');
    }
  }
  
  // good
  let test;
  if (currentUser) {
    test = () => {
      console.log('Yup.');
    };
  }

• 7.5 Never name a parameter arguments. This will take precedence over the arguments object that is given to every function scope.

  // bad
  function foo(name, options, arguments) {
    // ...
  }
  
  // good
  function foo(name, options, args) {
    // ...
  }

• 7.6 Never use arguments, opt to use rest syntax ... instead. eslint: prefer-rest-params

  Why? ... is explicit about which arguments you want pulled. Plus, rest arguments are a real Array, and not merely Array-like like arguments.

  // bad
  function concatenateAll() {
    const args = Array.prototype.slice.call(arguments);
    return args.join('');
  }
  
  // good
  function concatenateAll(...args) {
    return args.join('');
  }

• 7.7 Use default parameter syntax rather than mutating function arguments.

  // really bad
  function handleThings(opts) {
    // No! We shouldn’t mutate function arguments.
    // Double bad: if opts is falsy it'll be set to an object which may
    // be what you want but it can introduce subtle bugs.
    opts = opts || {};
    // ...
  }
  
  // still bad
  function handleThings(opts) {
    if (opts === void 0) {
      opts = {};
    }
    // ...
  }
  
  // good
  function handleThings(opts = {}) {
    // ...
  }

• 7.8 Avoid side effects with default parameters.

  Why? They are confusing to reason about.

  var b = 1;
  // bad
  function count(a = b++) {
    console.log(a);
  }
  count();  // 1
  count();  // 2
  count(3); // 3
  count();  // 3

• 7.9 Always put default parameters last.

  // bad
  function handleThings(opts = {}, name) {
    // ...
  }
  
  // good
  function handleThings(name, opts = {}) {
    // ...
  }

• 7.10 Never use the Function constructor to create a new function. eslint: no-new-func

  Why? Creating a function in this way evaluates a string similarly to eval(), which opens vulnerabilities.

  // bad
  var add = new Function('a', 'b', 'return a + b');
  
  // still bad
  var subtract = Function('a', 'b', 'return a - b');

• 7.11 Spacing in a function signature. eslint: space-before-function-paren space-before-blocks

@ZORO EXCEPTION: No space before parentheses.

> Why? Consistency is good, and you shouldn’t have to add or remove a space when adding or removing a name.

```javascript
// bad
const f = function(){};
const g = function (){};
const h = function() {};

// good
const x = function () {};
const y = function a() {};
```

• 7.12 Never mutate parameters. eslint: no-param-reassign

@ZORO EXCEPTION: Keep as rule but only as a warning.

> Why? Manipulating objects passed in as parameters can cause unwanted variable side effects in the original caller.

```javascript
// bad
function f1(obj) {
  obj.key = 1;
}

// good
function f2(obj) {
  const key = Object.prototype.hasOwnProperty.call(obj, 'key') ? obj.key : 1;
}
```

• 7.13 Never reassign parameters. eslint: no-param-reassign

  Why? Reassigning parameters can lead to unexpected behavior, especially when accessing the arguments object. It can also cause optimization issues, especially in V8.

  // bad
  function f1(a) {
    a = 1;
    // ...
  }
  
  function f2(a) {
    if (!a) { a = 1; }
    // ...
  }
  
  // good
  function f3(a) {
    const b = a || 1;
    // ...
  }
  
  function f4(a = 1) {
    // ...
  }

• 7.14 Prefer the use of the spread operator ... to call variadic functions. eslint: prefer-spread

  Why? It’s cleaner, you don’t need to supply a context, and you can not easily compose new with apply.

  // bad
  const x = [1, 2, 3, 4, 5];
  console.log.apply(console, x);
  
  // good
  const x = [1, 2, 3, 4, 5];
  console.log(...x);
  
  // bad
  new (Function.prototype.bind.apply(Date, [null, 2016, 8, 5]));
  
  // good
  new Date(...[2016, 8, 5]);

• 7.15 Functions with multiline signatures, or invocations, should be indented just like every other multiline list in this guide: with each item on a line by itself, with a trailing comma on the last item.

  // bad
  function foo(bar,
               baz,
               quux) {
    // ...
  }
  
  // good
  function foo(
    bar,
    baz,
    quux,
  ) {
    // ...
  }
  
  // bad
  console.log(foo,
    bar,
    baz);
  
  // good
  console.log(
    foo,
    bar,
    baz,
  );

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Arrow Functions

• 8.1 When you must use an anonymous function (as when passing an inline callback), use arrow function notation. eslint: prefer-arrow-callback, arrow-spacing jscs: requireArrowFunctions

@ZORO EXCEPTION: might not be possible with 3rd party libraries that set this on callbacks.

> Why? It creates a version of the function that executes in the context of `this`, which is usually what you want, and is a more concise syntax.

> Why not? If you have a fairly complicated function, you might move that logic out into its own named function expression.

```javascript
// bad
[1, 2, 3].map(function (x) {
  const y = x + 1;
  return x * y;
});

// good
[1, 2, 3].map((x) => {
  const y = x + 1;
  return x * y;
});
```

• 8.2 If the function body consists of a single statement returning an expression without side effects, omit the braces and use the implicit return. Otherwise, keep the braces and use a return statement. eslint: arrow-parens, arrow-body-style jscs: disallowParenthesesAroundArrowParam, requireShorthandArrowFunctions

  Why? Syntactic sugar. It reads well when multiple functions are chained together.

  // bad
  [1, 2, 3].map(number => {
    const nextNumber = number + 1;
    `A string containing the ${nextNumber}.`;
  });
  
  // good
  [1, 2, 3].map(number => `A string containing the ${number}.`);
  
  // good
  [1, 2, 3].map((number) => {
    const nextNumber = number + 1;
    return `A string containing the ${nextNumber}.`;
  });
  
  // good
  [1, 2, 3].map((number, index) => ({
    [index]: number,
  }));
  
  // No implicit return with side effects
  function foo(callback) {
    const val = callback();
    if (val === true) {
      // Do something if callback returns true
    }
  }
  
  let bool = false;
  
  // bad
  foo(() => bool = true);
  
  // good
  foo(() => {
    bool = true;
  });

• 8.3 In case the expression spans over multiple lines, wrap it in parentheses for better readability.

  Why? It shows clearly where the function starts and ends.

  // bad
  ['get', 'post', 'put'].map(httpMethod => Object.prototype.hasOwnProperty.call(
      httpMagicObjectWithAVeryLongName,
      httpMethod,
    )
  );
  
  // good
  ['get', 'post', 'put'].map(httpMethod => (
    Object.prototype.hasOwnProperty.call(
      httpMagicObjectWithAVeryLongName,
      httpMethod,
    )
  ));

• 8.4 If your function takes a single argument and doesn’t use braces, omit the parentheses. Otherwise, always include parentheses around arguments for clarity and consistency. Note: it is also acceptable to always use parentheses, in which case use the “always” option for eslint or do not include disallowParenthesesAroundArrowParam for jscs. eslint: arrow-parens jscs: disallowParenthesesAroundArrowParam

@ZORO EXCEPTION: Omit the parentheses when single argument.

> Why? Less visual clutter.

```javascript
// bad
[1, 2, 3].map((x) => x * x);

// good
[1, 2, 3].map(x => x * x);

// good
[1, 2, 3].map(number => (
  `A long string with the ${number}. It’s so long that we don’t want it to take up space on the .map line!`
));

// bad
[1, 2, 3].map(x => {
  const y = x + 1;
  return x * y;
});

// good
[1, 2, 3].map((x) => {
  const y = x + 1;
  return x * y;
});
```

• 8.5 Avoid confusing arrow function syntax (=>) with comparison operators (<=, >=). eslint: no-confusing-arrow

  // bad
  const itemHeight = item => item.height > 256 ? item.largeSize : item.smallSize;
  
  // bad
  const itemHeight = (item) => item.height > 256 ? item.largeSize : item.smallSize;
  
  // good
  const itemHeight = item => (item.height > 256 ? item.largeSize : item.smallSize);
  
  // good
  const itemHeight = (item) => {
    const { height, largeSize, smallSize } = item;
    return height > 256 ? largeSize : smallSize;
  };

⬆ back to top

Classes & Constructors

• 9.1 Always use class. Avoid manipulating prototype directly.

@ZORO NOTE: This has been agreed upon.

> Why? `class` syntax is more concise and easier to reason about.

```javascript
// bad
function Queue(contents = []) {
  this.queue = [...contents];
}
Queue.prototype.pop = function () {
  const value = this.queue[0];
  this.queue.splice(0, 1);
  return value;
};

// good
class Queue {
  constructor(contents = []) {
    this.queue = [...contents];
  }
  pop() {
    const value = this.queue[0];
    this.queue.splice(0, 1);
    return value;
  }
}
```

• 9.2 Use extends for inheritance.

  Why? It is a built-in way to inherit prototype functionality without breaking instanceof.

  // bad
  const inherits = require('inherits');
  function PeekableQueue(contents) {
    Queue.apply(this, contents);
  }
  inherits(PeekableQueue, Queue);
  PeekableQueue.prototype.peek = function () {
    return this.queue[0];
  };
  
  // good
  class PeekableQueue extends Queue {
    peek() {
      return this.queue[0];
    }
  }

• 9.3 Methods can return this to help with method chaining.

  // bad
  Jedi.prototype.jump = function () {
    this.jumping = true;
    return true;
  };
  
  Jedi.prototype.setHeight = function (height) {
    this.height = height;
  };
  
  const luke = new Jedi();
  luke.jump(); // => true
  luke.setHeight(20); // => undefined
  
  // good
  class Jedi {
    jump() {
      this.jumping = true;
      return this;
    }
  
    setHeight(height) {
      this.height = height;
      return this;
    }
  }
  
  const luke = new Jedi();
  
  luke.jump()
    .setHeight(20);

• 9.4 It’s okay to write a custom toString() method, just make sure it works successfully and causes no side effects.

  class Jedi {
    constructor(options = {}) {
      this.name = options.name || 'no name';
    }
  
    getName() {
      return this.name;
    }
  
    toString() {
      return `Jedi - ${this.getName()}`;
    }
  }

• 9.5 Classes have a default constructor if one is not specified. An empty constructor function or one that just delegates to a parent class is unnecessary. eslint: no-useless-constructor

  // bad
  class Jedi {
    constructor() {}
  
    getName() {
      return this.name;
    }
  }
  
  // bad
  class Rey extends Jedi {
    constructor(...args) {
      super(...args);
    }
  }
  
  // good
  class Rey extends Jedi {
    constructor(...args) {
      super(...args);
      this.name = 'Rey';
    }
  }

• 9.6 Avoid duplicate class members. eslint: no-dupe-class-members

  Why? Duplicate class member declarations will silently prefer the last one - having duplicates is almost certainly a bug.

  // bad
  class Foo {
    bar() { return 1; }
    bar() { return 2; }
  }
  
  // good
  class Foo {
    bar() { return 1; }
  }
  
  // good
  class Foo {
    bar() { return 2; }
  }

⬆ back to top

Modules

• 10.1 Always use modules (import/export) over a non-standard module system. You can always transpile to your preferred module system.

  Why? Modules are the future, let’s start using the future now.

  // bad
  const AirbnbStyleGuide = require('./AirbnbStyleGuide');
  module.exports = AirbnbStyleGuide.es6;
  
  // ok
  import AirbnbStyleGuide from './AirbnbStyleGuide';
  export default AirbnbStyleGuide.es6;
  
  // best
  import { es6 } from './AirbnbStyleGuide';
  export default es6;

• 10.2 Do not use wildcard imports.

@ZORO EXCEPTION: In tests wildcards are acceptable.

> Why? This makes sure you have a single default export.

```javascript
// bad
import * as AirbnbStyleGuide from './AirbnbStyleGuide';

// good
import AirbnbStyleGuide from './AirbnbStyleGuide';
```

• 10.3 And do not export directly from an import.

@ZORO NOTE: In addition, exports must be at the end of a file.

> Why? Although the one-liner is concise, having one clear way to import and one clear way to export makes things consistent.

```javascript
// bad
// filename es6.js
export { es6 as default } from './AirbnbStyleGuide';

// good
// filename es6.js
import { es6 } from './AirbnbStyleGuide';
export default es6;
```

• 10.4 Only import from a path in one place. eslint: no-duplicate-imports

  Why? Having multiple lines that import from the same path can make code harder to maintain.

  // bad
  import foo from 'foo';
  // … some other imports … //
  import { named1, named2 } from 'foo';
  
  // good
  import foo, { named1, named2 } from 'foo';
  
  // good
  import foo, {
    named1,
    named2,
  } from 'foo';

• 10.5 Do not export mutable bindings. eslint: import/no-mutable-exports

  Why? Mutation should be avoided in general, but in particular when exporting mutable bindings. While this technique may be needed for some special cases, in general, only constant references should be exported.

  // bad
  let foo = 3;
  export { foo };
  
  // good
  const foo = 3;
  export { foo };

• 10.6 In modules with a single export, prefer default export over named export. eslint: import/prefer-default-export

  Why? To encourage more files that only ever export one thing, which is better for readability and maintainability.

  // bad
  export function foo() {}
  
  // good
  export default function foo() {}

• 10.7 Put all imports above non-import statements. eslint: import/first

  Why? Since imports are hoisted, keeping them all at the top prevents surprising behavior.

  // bad
  import foo from 'foo';
  foo.init();
  
  import bar from 'bar';
  
  // good
  import foo from 'foo';
  import bar from 'bar';
  
  foo.init();

• 10.8 Multiline imports should be indented just like multiline array and object literals.

@ZORO EXCEPTION: Ignore as multiline imports aren't allowed.

> Why? The curly braces follow the same indentation rules as every other curly brace block in the style guide, as do the trailing commas.

```javascript
// bad
import {longNameA, longNameB, longNameC, longNameD, longNameE} from 'path';

// good
import {
  longNameA,
  longNameB,
  longNameC,
  longNameD,
  longNameE,
} from 'path';
```

• 10.9 Disallow Webpack loader syntax in module import statements. eslint: import/no-webpack-loader-syntax

@ZORO EXCEPTION: Ignore because jspm requires this. *

> Why? Since using Webpack syntax in the imports couples the code to a module bundler. Prefer using the loader syntax in `webpack.config.js`.

```javascript
// bad
import fooSass from 'css!sass!foo.scss';
import barCss from 'style!css!bar.css';

// good
import fooSass from 'foo.scss';
import barCss from 'bar.css';
```

⬆ back to top

Iterators and Generators

• 11.1 Don’t use iterators. Prefer JavaScript’s higher-order functions instead of loops like for-in or for-of. eslint: no-iterator no-restricted-syntax

  Why? This enforces our immutable rule. Dealing with pure functions that return values is easier to reason about than side effects.

  Use map() / every() / filter() / find() / findIndex() / reduce() / some() / ... to iterate over arrays, and Object.keys() / Object.values() / Object.entries() to produce arrays so you can iterate over objects.

  const numbers = [1, 2, 3, 4, 5];
  
  // bad
  let sum = 0;
  for (let num of numbers) {
    sum += num;
  }
  sum === 15;
  
  // good
  let sum = 0;
  numbers.forEach((num) => {
    sum += num;
  });
  sum === 15;
  
  // best (use the functional force)
  const sum = numbers.reduce((total, num) => total + num, 0);
  sum === 15;
  
  // bad
  const increasedByOne = [];
  for (let i = 0; i < numbers.length; i++) {
    increasedByOne.push(numbers[i] + 1);
  }
  
  // good
  const increasedByOne = [];
  numbers.forEach((num) => {
    increasedByOne.push(num + 1);
  });
  
  // best (keeping it functional)
  const increasedByOne = numbers.map(num => num + 1);

• 11.2 Don’t use generators for now.

  Why? They don’t transpile well to ES5.

• 11.3 If you must use generators, or if you disregard our advice, make sure their function signature is spaced properly. eslint: generator-star-spacing

  Why? function and * are part of the same conceptual keyword - * is not a modifier for function, function* is a unique construct, different from function.

  // bad
  function * foo() {
    // ...
  }
  
  // bad
  const bar = function * () {
    // ...
  };
  
  // bad
  const baz = function *() {
    // ...
  };
  
  // bad
  const quux = function*() {
    // ...
  };
  
  // bad
  function*foo() {
    // ...
  }
  
  // bad
  function *foo() {
    // ...
  }
  
  // very bad
  function
  *
  foo() {
    // ...
  }
  
  // very bad
  const wat = function
  *
  () {
    // ...
  };
  
  // good
  function* foo() {
    // ...
  }
  
  // good
  const foo = function* () {
    // ...
  };

⬆ back to top

Properties

• 12.1 Use dot notation when accessing properties. eslint: dot-notation jscs: requireDotNotation

  const luke = {
    jedi: true,
    age: 28,
  };
  
  // bad
  const isJedi = luke['jedi'];
  
  // good
  const isJedi = luke.jedi;

• 12.2 Use bracket notation [] when accessing properties with a variable.

  const luke = {
    jedi: true,
    age: 28,
  };
  
  function getProp(prop) {
    return luke[prop];
  }
  
  const isJedi = getProp('jedi');

• 12.3 Use exponentiation operator ** when calculating exponentiations. eslint: no-restricted-properties.

  // bad
  const binary = Math.pow(2, 10);
  
  // good
  const binary = 2 ** 10;

⬆ back to top

Variables

• 13.1 Always use const or let to declare variables. Not doing so will result in global variables. We want to avoid polluting the global namespace. Captain Planet warned us of that. eslint: no-undef prefer-const

  // bad
  superPower = new SuperPower();
  
  // good
  const superPower = new SuperPower();

• 13.2 Use one const or let declaration per variable. eslint: one-var jscs: disallowMultipleVarDecl

  Why? It’s easier to add new variable declarations this way, and you never have to worry about swapping out a ; for a , or introducing punctuation-only diffs. You can also step through each declaration with the debugger, instead of jumping through all of them at once.

  // bad
  const items = getItems(),
      goSportsTeam = true,
      dragonball = 'z';
  
  // bad
  // (compare to above, and try to spot the mistake)
  const items = getItems(),
      goSportsTeam = true;
      dragonball = 'z';
  
  // good
  const items = getItems();
  const goSportsTeam = true;
  const dragonball = 'z';

• 13.3 Group all your consts and then group all your lets.

  Why? This is helpful when later on you might need to assign a variable depending on one of the previous assigned variables.

  // bad
  let i, len, dragonball,
      items = getItems(),
      goSportsTeam = true;
  
  // bad
  let i;
  const items = getItems();
  let dragonball;
  const goSportsTeam = true;
  let len;
  
  // good
  const goSportsTeam = true;
  const items = getItems();
  let dragonball;
  let i;
  let length;

• 13.4 Assign variables where you need them, but place them in a reasonable place.

  Why? let and const are block scoped and not function scoped.

  // bad - unnecessary function call
  function checkName(hasName) {
    const name = getName();
  
    if (hasName === 'test') {
      return false;
    }
  
    if (name === 'test') {
      this.setName('');
      return false;
    }
  
    return name;
  }
  
  // good
  function checkName(hasName) {
    if (hasName === 'test') {
      return false;
    }
  
    const name = getName();
  
    if (name === 'test') {
      this.setName('');
      return false;
    }
  
    return name;
  }

• 13.5 Don’t chain variable assignments. eslint: no-multi-assign

  Why? Chaining variable assignments creates implicit global variables.

  // bad
  (function example() {
    // JavaScript interprets this as
    // let a = ( b = ( c = 1 ) );
    // The let keyword only applies to variable a; variables b and c become
    // global variables.
    let a = b = c = 1;
  }());
  
  console.log(a); // throws ReferenceError
  console.log(b); // 1
  console.log(c); // 1
  
  // good
  (function example() {
    let a = 1;
    let b = a;
    let c = a;
  }());
  
  console.log(a); // throws ReferenceError
  console.log(b); // throws ReferenceError
  console.log(c); // throws ReferenceError
  
  // the same applies for `const`

• 13.6 Avoid using unary increments and decrements (++, --). eslint no-plusplus

@ZORO EXCEPTION: Ignore.

> Why? Per the eslint documentation, unary increment and decrement statements are subject to automatic semicolon insertion and can cause silent errors with incrementing or decrementing values within an application. It is also more expressive to mutate your values with statements like `num += 1` instead of `num++` or `num ++`. Disallowing unary increment and decrement statements also prevents you from pre-incrementing/pre-decrementing values unintentionally which can also cause unexpected behavior in your programs.

```javascript
// bad

const array = [1, 2, 3];
let num = 1;
num++;
--num;

let sum = 0;
let truthyCount = 0;
for (let i = 0; i < array.length; i++) {
  let value = array[i];
  sum += value;
  if (value) {
    truthyCount++;
  }
}

// good

const array = [1, 2, 3];
let num = 1;
num += 1;
num -= 1;

const sum = array.reduce((a, b) => a + b, 0);
const truthyCount = array.filter(Boolean).length;
```

⬆ back to top

Hoisting

• 14.1 var declarations get hoisted to the top of their closest enclosing function scope, their assignment does not. const and let declarations are blessed with a new concept called Temporal Dead Zones (TDZ). It’s important to know why typeof is no longer safe.

  // we know this wouldn’t work (assuming there
  // is no notDefined global variable)
  function example() {
    console.log(notDefined); // => throws a ReferenceError
  }
  
  // creating a variable declaration after you
  // reference the variable will work due to
  // variable hoisting. Note: the assignment
  // value of `true` is not hoisted.
  function example() {
    console.log(declaredButNotAssigned); // => undefined
    var declaredButNotAssigned = true;
  }
  
  // the interpreter is hoisting the variable
  // declaration to the top of the scope,
  // which means our example could be rewritten as:
  function example() {
    let declaredButNotAssigned;
    console.log(declaredButNotAssigned); // => undefined
    declaredButNotAssigned = true;
  }
  
  // using const and let
  function example() {
    console.log(declaredButNotAssigned); // => throws a ReferenceError
    console.log(typeof declaredButNotAssigned); // => throws a ReferenceError
    const declaredButNotAssigned = true;
  }

• 14.2 Anonymous function expressions hoist their variable name, but not the function assignment.

  function example() {
    console.log(anonymous); // => undefined
  
    anonymous(); // => TypeError anonymous is not a function
  
    var anonymous = function () {
      console.log('anonymous function expression');
    };
  }

• 14.3 Named function expressions hoist the variable name, not the function name or the function body.

  function example() {
    console.log(named); // => undefined
  
    named(); // => TypeError named is not a function
  
    superPower(); // => ReferenceError superPower is not defined
  
    var named = function superPower() {
      console.log('Flying');
    };
  }
  
  // the same is true when the function name
  // is the same as the variable name.
  function example() {
    console.log(named); // => undefined
  
    named(); // => TypeError named is not a function
  
    var named = function named() {
      console.log('named');
    };
  }

• 14.4 Function declarations hoist their name and the function body.

  function example() {
    superPower(); // => Flying
  
    function superPower() {
      console.log('Flying');
    }
  }

• For more information refer to JavaScript Scoping & Hoisting by Ben Cherry.

⬆ back to top

Comparison Operators & Equality

• 15.1 Use === and !== over == and !=. eslint: eqeqeq

• 15.2 Conditional statements such as the if statement evaluate their expression using coercion with the ToBoolean abstract method and always follow these simple rules:

  • Objects evaluate to true
  • Undefined evaluates to false
  • Null evaluates to false
  • Booleans evaluate to the value of the boolean
  • Numbers evaluate to false if +0, -0, or NaN, otherwise true
  • Strings evaluate to false if an empty string '', otherwise true

  if ([0] && []) {
    // true
    // an array (even an empty one) is an object, objects will evaluate to true
  }

• 15.3 Use shortcuts for booleans, but explicit comparisons for strings and numbers.

  // bad
  if (isValid === true) {
    // ...
  }
  
  // good
  if (isValid) {
    // ...
  }
  
  // bad
  if (name) {
    // ...
  }
  
  // good
  if (name !== '') {
    // ...
  }
  
  // bad
  if (collection.length) {
    // ...
  }
  
  // good
  if (collection.length > 0) {
    // ...
  }

• 15.4 For more information see Truth Equality and JavaScript by Angus Croll.

• 15.5 Use braces to create blocks in case and default clauses that contain lexical declarations (e.g. let, const, function, and class). eslint: no-case-declarations

  Why? Lexical declarations are visible in the entire switch block but only get initialized when assigned, which only happens when its case is reached. This causes problems when multiple case clauses attempt to define the same thing.

  // bad
  switch (foo) {
    case 1:
      let x = 1;
      break;
    case 2:
      const y = 2;
      break;
    case 3:
      function f() {
        // ...
      }
      break;
    default:
      class C {}
  }
  
  // good
  switch (foo) {
    case 1: {
      let x = 1;
      break;
    }
    case 2: {
      const y = 2;
      break;
    }
    case 3: {
      function f() {
        // ...
      }
      break;
    }
    case 4:
      bar();
      break;
    default: {
      class C {}
    }
  }

• 15.6 Ternaries should not be nested and generally be single line expressions. eslint: no-nested-ternary

  // bad
  const foo = maybe1 > maybe2
    ? "bar"
    : value1 > value2 ? "baz" : null;
  
  // split into 2 separated ternary expressions
  const maybeNull = value1 > value2 ? 'baz' : null;
  
  // better
  const foo = maybe1 > maybe2
    ? 'bar'
    : maybeNull;
  
  // best
  const foo = maybe1 > maybe2 ? 'bar' : maybeNull;

• 15.7 Avoid unneeded ternary statements. eslint: no-unneeded-ternary

@ZORO NOTE: This has been agreed upon.

```javascript
// bad
const foo = a ? a : b;
const bar = c ? true : false;
const baz = c ? false : true;

// good
const foo = a || b;
const bar = !!c;
const baz = !c;
```

• 15.8 When mixing operators, enclose them in parentheses. The only exception is the standard arithmetic operators (+, -, *, & /) since their precedence is broadly understood. eslint: no-mixed-operators

@ZORO NOTE: Parentheses preferred for clarity.

> Why? This improves readability and clarifies the developer’s intention.

```javascript
// bad
const foo = a && b < 0 || c > 0 || d + 1 === 0;

// bad
const bar = a ** b - 5 % d;

// bad
// one may be confused into thinking (a || b) && c
if (a || b && c) {
  return d;
}

// good
const foo = (a && b < 0) || c > 0 || (d + 1 === 0);

// good
const bar = (a ** b) - (5 % d);

// good
if (a || (b && c)) {
  return d;
}

// good
const bar = a + b / c * d;
```

⬆ back to top

Blocks

• 16.1 Use braces with all multi-line blocks. eslint: nonblock-statement-body-position

  // bad
  if (test)
    return false;
  
  // good
  if (test) return false;
  
  // good
  if (test) {
    return false;
  }
  
  // bad
  function foo() { return false; }
  
  // good
  function bar() {
    return false;
  }

• 16.2 If you're using multi-line blocks with if and else, put else on the same line as your if block’s closing brace. eslint: brace-style jscs: disallowNewlineBeforeBlockStatements

  // bad
  if (test) {
    thing1();
    thing2();
  }
  else {
    thing3();
  }
  
  // good
  if (test) {
    thing1();
    thing2();
  } else {
    thing3();
  }

• 16.3 If an if block always executes a return statement, the subsequent else block is unnecessary. A return in an else if block following an if block that contains a return can be separated into multiple if blocks. eslint: no-else-return

  // bad
  function foo() {
    if (x) {
      return x;
    } else {
      return y;
    }
  }
  
  // bad
  function cats() {
    if (x) {
      return x;
    } else if (y) {
      return y;
    }
  }
  
  // bad
  function dogs() {
    if (x) {
      return x;
    } else {
      if (y) {
        return y;
      }
    }
  }
  
  // good
  function foo() {
    if (x) {
      return x;
    }
  
    return y;
  }
  
  // good
  function cats() {
    if (x) {
      return x;
    }
  
    if (y) {
      return y;
    }
  }
  
  //good
  function dogs(x) {
    if (x) {
      if (z) {
        return y;
      }
    } else {
      return z;
    }
  }

⬆ back to top

Control Statements

• 17.1 In case your control statement (if, while etc.) gets too long or exceeds the maximum line length, each (grouped) condition could be put into a new line. The logical operator should begin the line.

  Why? Requiring operators at the beginning of the line keeps the operators aligned and follows a pattern similar to method chaining. This also improves readability by making it easier to visually follow complex logic.

  // bad
  if ((foo === 123 || bar === 'abc') && doesItLookGoodWhenItBecomesThatLong() && isThisReallyHappening()) {
    thing1();
  }
  
  // bad
  if (foo === 123 &&
    bar === 'abc') {
    thing1();
  }
  
  // bad
  if (foo === 123
    && bar === 'abc') {
    thing1();
  }
  
  // bad
  if (
    foo === 123 &&
    bar === 'abc'
  ) {
    thing1();
  }
  
  // good
  if (
    foo === 123
    && bar === 'abc'
  ) {
    thing1();
  }
  
  // good
  if (
    (foo === 123 || bar === "abc")
    && doesItLookGoodWhenItBecomesThatLong()
    && isThisReallyHappening()
  ) {
    thing1();
  }
  
  // good
  if (foo === 123 && bar === 'abc') {
    thing1();
  }

⬆ back to top

Comments

• 18.1 Use /** ... */ for multi-line comments.

  // bad
  // make() returns a new element
  // based on the passed in tag name
  //
  // @param {String} tag
  // @return {Element} element
  function make(tag) {
  
    // ...
  
    return element;
  }
  
  // good
  /**
   * make() returns a new element
   * based on the passed-in tag name
   */
  function make(tag) {
  
    // ...
  
    return element;
  }

• 18.2 Use // for single line comments. Place single line comments on a newline above the subject of the comment. Put an empty line before the comment unless it’s on the first line of a block.

@ZORO EXCEPTION: ignore, same line comments acceptable except when it exceeds max line length

```javascript
// bad
const active = true;  // is current tab

// good
// is current tab
const active = true;

// bad
function getType() {
  console.log('fetching type...');
  // set the default type to 'no type'
  const type = this.type || 'no type';

  return type;
}

// good
function getType() {
  console.log('fetching type...');

  // set the default type to 'no type'
  const type = this.type || 'no type';

  return type;
}

// also good
function getType() {
  // set the default type to 'no type'
  const type = this.type || 'no type';

  return type;
}
```

• 18.3 Start all comments with a space to make it easier to read. eslint: spaced-comment

  // bad
  //is current tab
  const active = true;
  
  // good
  // is current tab
  const active = true;
  
  // bad
  /**
   *make() returns a new element
   *based on the passed-in tag name
   */
  function make(tag) {
  
    // ...
  
    return element;
  }
  
  // good
  /**
   * make() returns a new element
   * based on the passed-in tag name
   */
  function make(tag) {
  
    // ...
  
    return element;
  }

• 18.4 Prefixing your comments with FIXME or TODO helps other developers quickly understand if you're pointing out a problem that needs to be revisited, or if you're suggesting a solution to the problem that needs to be implemented. These are different than regular comments because they are actionable. The actions are FIXME: -- need to figure this out or TODO: -- need to implement.

@ZORO EXCEPTION: REQUIRES FURTHER CLARIFICATION WITH JOE

• 18.5 Use // FIXME: to annotate problems.

  class Calculator extends Abacus {
    constructor() {
      super();
  
      // FIXME: shouldn’t use a global here
      total = 0;
    }
  }

• 18.6 Use // TODO: to annotate solutions to problems.

  class Calculator extends Abacus {
    constructor() {
      super();
  
      // TODO: total should be configurable by an options param
      this.total = 0;
    }
  }

⬆ back to top

Whitespace

• 19.1 Use soft tabs (space character) set to 2 spaces. eslint: indent jscs: validateIndentation

  // bad
  function foo() {
  ∙∙∙∙let name;
  }
  
  // bad
  function bar() {
  ∙let name;
  }
  
  // good
  function baz() {
  ∙∙let name;
  }

• 19.2 Place 1 space before the leading brace. eslint: space-before-blocks jscs: requireSpaceBeforeBlockStatements

  // bad
  function test(){
    console.log('test');
  }
  
  // good
  function test() {
    console.log('test');
  }
  
  // bad
  dog.set('attr',{
    age: '1 year',
    breed: 'Bernese Mountain Dog',
  });
  
  // good
  dog.set('attr', {
    age: '1 year',
    breed: 'Bernese Mountain Dog',
  });

• 19.3 Place 1 space before the opening parenthesis in control statements (if, while etc.). Place no space between the argument list and the function name in function calls and declarations. eslint: keyword-spacing jscs: requireSpaceAfterKeywords

  // bad
  if(isJedi) {
    fight ();
  }
  
  // good
  if (isJedi) {
    fight();
  }
  
  // bad
  function fight () {
    console.log ('Swooosh!');
  }
  
  // good
  function fight() {
    console.log('Swooosh!');
  }

• 19.4 Set off operators with spaces. eslint: space-infix-ops jscs: requireSpaceBeforeBinaryOperators, requireSpaceAfterBinaryOperators

  // bad
  const x=y+5;
  
  // good
  const x = y + 5;

• 19.5 End files with a single newline character. eslint: eol-last

  // bad
  import { es6 } from './AirbnbStyleGuide';
    // ...
  export default es6;

  // bad
  import { es6 } from './AirbnbStyleGuide';
    // ...
  export default es6;↵
  ↵

  // good
  import { es6 } from './AirbnbStyleGuide';
    // ...
  export default es6;↵

• 19.6 Use indentation when making long method chains (more than 2 method chains). Use a leading dot, which emphasizes that the line is a method call, not a new statement. eslint: newline-per-chained-call no-whitespace-before-property

  @ZORO NOTE: Only to be implemented if auto-formatting or minimum effort is possible.

  // bad
  $('#items').find('.selected').highlight().end().find('.open').updateCount();
  
  // bad
  $('#items').
    find('.selected').
      highlight().
      end().
    find('.open').
      updateCount();
  
  // good
  $('#items')
    .find('.selected')
      .highlight()
      .end()
    .find('.open')
      .updateCount();
  
  // bad
  const leds = stage.selectAll('.led').data(data).enter().append('svg:svg').classed('led', true)
      .attr('width', (radius + margin) * 2).append('svg:g')
      .attr('transform', `translate(${radius + margin},${radius + margin})`)
      .call(tron.led);
  
  // good
  const leds = stage.selectAll('.led')
      .data(data)
    .enter().append('svg:svg')
      .classed('led', true)
      .attr('width', (radius + margin) * 2)
    .append('svg:g')
      .attr('transform', `translate(${radius + margin},${radius + margin})`)
      .call(tron.led);
  
  // good
  const leds = stage.selectAll('.led').data(data);

• 19.7 Leave a blank line after blocks and before the next statement. jscs: requirePaddingNewLinesAfterBlocks

@ZORO NOTE: This has been agreed on.

```javascript
// bad
if (foo) {
  return bar;
}
return baz;

// good
if (foo) {
  return bar;
}

return baz;

// bad
const obj = {
  foo() {
  },
  bar() {
  },
};
return obj;

// good
const obj = {
  foo() {
  },

  bar() {
  },
};

return obj;

// bad
const arr = [
  function foo() {
  },
  function bar() {
  },
];
return arr;

// good
const arr = [
  function foo() {
  },

  function bar() {
  },
];

return arr;
```

• 19.8 Do not pad your blocks with blank lines. eslint: padded-blocks jscs: disallowPaddingNewlinesInBlocks

@ZORO NOTE: This has been agreed on.

```javascript
// bad
function bar() {

  console.log(foo);

}

// bad
if (baz) {

  console.log(qux);
} else {
  console.log(foo);

}

// bad
class Foo {

  constructor(bar) {
    this.bar = bar;
  }
}

// good
function bar() {
  console.log(foo);
}

// good
if (baz) {
  console.log(qux);
} else {
  console.log(foo);
}
```

• 19.9 Do not add spaces inside parentheses. eslint: space-in-parens jscs: disallowSpacesInsideParentheses

  // bad
  function bar( foo ) {
    return foo;
  }
  
  // good
  function bar(foo) {
    return foo;
  }
  
  // bad
  if ( foo ) {
    console.log(foo);
  }
  
  // good
  if (foo) {
    console.log(foo);
  }

• 19.10 Do not add spaces inside brackets. eslint: array-bracket-spacing jscs: disallowSpacesInsideArrayBrackets

  // bad
  const foo = [ 1, 2, 3 ];
  console.log(foo[ 0 ]);
  
  // good
  const foo = [1, 2, 3];
  console.log(foo[0]);

• 19.11 Add spaces inside curly braces. eslint: object-curly-spacing jscs: requireSpacesInsideObjectBrackets

@ZORO EXCEPTION: Ignore, do the opposite.

```javascript
// bad
const foo = {clark: 'kent'};

// good
const foo = { clark: 'kent' };
```

• 19.12 Avoid having lines of code that are longer than 100 characters (including whitespace). Note: per above, long strings are exempt from this rule, and should not be broken up. eslint: max-len jscs: maximumLineLength

@ZORO EXCEPTION: 120 character limit to be implemented instead.

> Why? This ensures readability and maintainability.

```javascript
// bad
const foo = jsonData && jsonData.foo && jsonData.foo.bar && jsonData.foo.bar.baz && jsonData.foo.bar.baz.quux && jsonData.foo.bar.baz.quux.xyzzy;

// bad
$.ajax({ method: 'POST', url: 'https://airbnb.com/', data: { name: 'John' } }).done(() => console.log('Congratulations!')).fail(() => console.log('You have failed this city.'));

// good
const foo = jsonData
  && jsonData.foo
  && jsonData.foo.bar
  && jsonData.foo.bar.baz
  && jsonData.foo.bar.baz.quux
  && jsonData.foo.bar.baz.quux.xyzzy;

// good
$.ajax({
  method: 'POST',
  url: 'https://airbnb.com/',
  data: { name: 'John' },
})
  .done(() => console.log('Congratulations!'))
  .fail(() => console.log('You have failed this city.'));
```

⬆ back to top

Commas

• 20.1 Leading commas: Nope. eslint: comma-style jscs: requireCommaBeforeLineBreak

@ZORO NOTE: This has been agreed upon.

```javascript
// bad
const story = [
    once
  , upon
  , aTime
];

// good
const story = [
  once,
  upon,
  aTime,
];

// bad
const hero = {
    firstName: 'Ada'
  , lastName: 'Lovelace'
  , birthYear: 1815
  , superPower: 'computers'
};

// good
const hero = {
  firstName: 'Ada',
  lastName: 'Lovelace',
  birthYear: 1815,
  superPower: 'computers',
};
```

• 20.2 Additional trailing comma: Yup. eslint: comma-dangle jscs: requireTrailingComma

  Why? This leads to cleaner git diffs. Also, transpilers like Babel will remove the additional trailing comma in the transpiled code which means you don’t have to worry about the trailing comma problem in legacy browsers.

  // bad - git diff without trailing comma
  const hero = {
       firstName: 'Florence',
  -    lastName: 'Nightingale'
  +    lastName: 'Nightingale',
  +    inventorOf: ['coxcomb chart', 'modern nursing']
  };
  
  // good - git diff with trailing comma
  const hero = {
       firstName: 'Florence',
       lastName: 'Nightingale',
  +    inventorOf: ['coxcomb chart', 'modern nursing'],
  };

  // bad
  const hero = {
    firstName: 'Dana',
    lastName: 'Scully'
  };
  
  const heroes = [
    'Batman',
    'Superman'
  ];
  
  // good
  const hero = {
    firstName: 'Dana',
    lastName: 'Scully',
  };
  
  const heroes = [
    'Batman',
    'Superman',
  ];
  
  // bad
  function createHero(
    firstName,
    lastName,
    inventorOf
  ) {
    // does nothing
  }
  
  // good
  function createHero(
    firstName,
    lastName,
    inventorOf,
  ) {
    // does nothing
  }
  
  // good (note that a comma must not appear after a "rest" element)
  function createHero(
    firstName,
    lastName,
    inventorOf,
    ...heroArgs
  ) {
    // does nothing
  }
  
  // bad
  createHero(
    firstName,
    lastName,
    inventorOf
  );
  
  // good
  createHero(
    firstName,
    lastName,
    inventorOf,
  );
  
  // good (note that a comma must not appear after a "rest" element)
  createHero(
    firstName,
    lastName,
    inventorOf,
    ...heroArgs
  );

⬆ back to top

Semicolons

• 21.1 Yup. eslint: semi jscs: requireSemicolons

  Why? When JavaScript encounters a line break without a semicolon, it uses a set of rules called Automatic Semicolon Insertion to determine whether or not it should regard that line break as the end of a statement, and (as the name implies) place a semicolon into your code before the line break if it thinks so. ASI contains a few eccentric behaviors, though, and your code will break if JavaScript misinterprets your line break. These rules will become more complicated as new features become a part of JavaScript. Explicitly terminating your statements and configuring your linter to catch missing semicolons will help prevent you from encountering issues.

  // bad - raises exception
  const luke = {}
  const leia = {}
  [luke, leia].forEach(jedi => jedi.father = 'vader')
  
  // bad - raises exception
  const reaction = "No! That's impossible!"
  (async function meanwhileOnTheFalcon(){
    // handle `leia`, `lando`, `chewie`, `r2`, `c3p0`
    // ...
  }())
  
  // bad - returns `undefined` instead of the value on the next line - always happens when `return` is on a line by itself because of ASI!
  function foo() {
    return
      'search your feelings, you know it to be foo'
  }
  
  // good
  const luke = {};
  const leia = {};
  [luke, leia].forEach((jedi) => {
    jedi.father = 'vader';
  });
  
  // good
  const reaction = "No! That's impossible!";
  (async function meanwhileOnTheFalcon(){
    // handle `leia`, `lando`, `chewie`, `r2`, `c3p0`
    // ...
  }());
  
  // good
  function foo() {
    return 'search your feelings, you know it to be foo';
  }

  Read more.

⬆ back to top

Type Casting & Coercion

• 22.1 Perform type coercion at the beginning of the statement.

• 22.2 Strings: eslint: no-new-wrappers

  // => this.reviewScore = 9;
  
  // bad
  const totalScore = new String(this.reviewScore); // typeof totalScore is "object" not "string"
  
  // bad
  const totalScore = this.reviewScore + ''; // invokes this.reviewScore.valueOf()
  
  // bad
  const totalScore = this.reviewScore.toString(); // isn’t guaranteed to return a string
  
  // good
  const totalScore = String(this.reviewScore);

• 22.3 Numbers: Use Number for type casting and parseInt always with a radix for parsing strings. eslint: radix no-new-wrappers

  const inputValue = '4';
  
  // bad
  const val = new Number(inputValue);
  
  // bad
  const val = +inputValue;
  
  // bad
  const val = inputValue >> 0;
  
  // bad
  const val = parseInt(inputValue);
  
  // good
  const val = Number(inputValue);
  
  // good
  const val = parseInt(inputValue, 10);

• 22.4 If for whatever reason you are doing something wild and parseInt is your bottleneck and need to use Bitshift for performance reasons, leave a comment explaining why and what you're doing.

  // good
  /**
   * parseInt was the reason my code was slow.
   * Bitshifting the String to coerce it to a
   * Number made it a lot faster.
   */
  const val = inputValue >> 0;

• 22.5 Note: Be careful when using bitshift operations. Numbers are represented as 64-bit values, but bitshift operations always return a 32-bit integer (source). Bitshift can lead to unexpected behavior for integer values larger than 32 bits. Discussion. Largest signed 32-bit Int is 2,147,483,647:

  2147483647 >> 0; // => 2147483647
  2147483648 >> 0; // => -2147483648
  2147483649 >> 0; // => -2147483647

• 22.6 Booleans: eslint: no-new-wrappers

  const age = 0;
  
  // bad
  const hasAge = new Boolean(age);
  
  // good
  const hasAge = Boolean(age);
  
  // best
  const hasAge = !!age;

⬆ back to top

Naming Conventions

• 23.1 Avoid single letter names. Be descriptive with your naming. eslint: id-length

@ZORO EXCEPTION: This has been agreed upon with exceptions for 3rd party libraries and the global z object.

```javascript
// bad
function q() {
  // ...
}

// good
function query() {
  // ...
}
```

• 23.2 Use camelCase when naming objects, functions, and instances. eslint: camelcase jscs: requireCamelCaseOrUpperCaseIdentifiers

  // bad
  const OBJEcttsssss = {};
  const this_is_my_object = {};
  function c() {}
  
  // good
  const thisIsMyObject = {};
  function thisIsMyFunction() {}

• 23.3 Use PascalCase only when naming constructors or classes. eslint: new-cap jscs: requireCapitalizedConstructors

  // bad
  function user(options) {
    this.name = options.name;
  }
  
  const bad = new user({
    name: 'nope',
  });
  
  // good
  class User {
    constructor(options) {
      this.name = options.name;
    }
  }
  
  const good = new User({
    name: 'yup',
  });

• 23.4 Do not use trailing or leading underscores. eslint: no-underscore-dangle jscs: disallowDanglingUnderscores

  Why? JavaScript does not have the concept of privacy in terms of properties or methods. Although a leading underscore is a common convention to mean “private”, in fact, these properties are fully public, and as such, are part of your public API contract. This convention might lead developers to wrongly think that a change won’t count as breaking, or that tests aren’t needed. tl;dr: if you want something to be “private”, it must not be observably present.

  // bad
  this.__firstName__ = 'Panda';
  this.firstName_ = 'Panda';
  this._firstName = 'Panda';
  
  // good
  this.firstName = 'Panda';

• 23.5 Don’t save references to this. Use arrow functions or Function#bind. jscs: disallowNodeTypes

@ZORO EXCEPTION: Follow this rule where possible.

```javascript
// bad
function foo() {
  const self = this;
  return function () {
    console.log(self);
  };
}

// bad
function foo() {
  const that = this;
  return function () {
    console.log(that);
  };
}

// good
function foo() {
  return () => {
    console.log(this);
  };
}
```

• 23.6 A base filename should exactly match the name of its default export.

  // file 1 contents
  class CheckBox {
    // ...
  }
  export default CheckBox;
  
  // file 2 contents
  export default function fortyTwo() { return 42; }
  
  // file 3 contents
  export default function insideDirectory() {}
  
  // in some other file
  // bad
  import CheckBox from './checkBox'; // PascalCase import/export, camelCase filename
  import FortyTwo from './FortyTwo'; // PascalCase import/filename, camelCase export
  import InsideDirectory from './InsideDirectory'; // PascalCase import/filename, camelCase export
  
  // bad
  import CheckBox from './check_box'; // PascalCase import/export, snake_case filename
  import forty_two from './forty_two'; // snake_case import/filename, camelCase export
  import inside_directory from './inside_directory'; // snake_case import, camelCase export
  import index from './inside_directory/index'; // requiring the index file explicitly
  import insideDirectory from './insideDirectory/index'; // requiring the index file explicitly
  
  // good
  import CheckBox from './CheckBox'; // PascalCase export/import/filename
  import fortyTwo from './fortyTwo'; // camelCase export/import/filename
  import insideDirectory from './insideDirectory'; // camelCase export/import/directory name/implicit "index"
  // ^ supports both insideDirectory.js and insideDirectory/index.js

• 23.7 Use camelCase when you export-default a function. Your filename should be identical to your function’s name.

  function makeStyleGuide() {
    // ...
  }
  
  export default makeStyleGuide;

• 23.8 Use PascalCase when you export a constructor / class / singleton / function library / bare object.

  const AirbnbStyleGuide = {
    es6: {
    },
  };
  
  export default AirbnbStyleGuide;

• 23.9 Acronyms and initialisms should always be all capitalized, or all lowercased.

@ZORO EXCEPTION: Ignore, continue using pascal casing for acronyms and initialisms.

> Why? Names are for readability, not to appease a computer algorithm.

```javascript
// bad
import SmsContainer from './containers/SmsContainer';

// bad
const HttpRequests = [
  // ...
];

// good
import SMSContainer from './containers/SMSContainer';

// good
const HTTPRequests = [
  // ...
];

// also good
const httpRequests = [
  // ...
];

// best
import TextMessageContainer from './containers/TextMessageContainer';

// best
const requests = [
  // ...
];
```

⬆ back to top

Accessors

• 24.1 Accessor functions for properties are not required.

• 24.2 Do not use JavaScript getters/setters as they cause unexpected side effects and are harder to test, maintain, and reason about. Instead, if you do make accessor functions, use getVal() and setVal('hello').

@ZORO EXCEPTION: Ignore.

```javascript
// bad
class Dragon {
  get age() {
    // ...
  }

  set age(value) {
    // ...
  }
}

// good
class Dragon {
  getAge() {
    // ...
  }

  setAge(value) {
    // ...
  }
}
```

• 24.3 If the property/method is a boolean, use isVal() or hasVal().

  // bad
  if (!dragon.age()) {
    return false;
  }
  
  // good
  if (!dragon.hasAge()) {
    return false;
  }

• 24.4 It’s okay to create get() and set() functions, but be consistent.

@ZORO EXCEPTION: Ignore.

```javascript
class Jedi {
  constructor(options = {}) {
    const lightsaber = options.lightsaber || 'blue';
    this.set('lightsaber', lightsaber);
  }

  set(key, val) {
    this[key] = val;
  }

  get(key) {
    return this[key];
  }
}
```

⬆ back to top

Events

• 25.1 When attaching data payloads to events (whether DOM events or something more proprietary like Backbone events), pass an object literal (also known as a "hash") instead of a raw value. This allows a subsequent contributor to add more data to the event payload without finding and updating every handler for the event. For example, instead of:

@ZORO NOTE: This has been agreed upon.

```javascript
// bad
$(this).trigger('listingUpdated', listing.id);

// ...

$(this).on('listingUpdated', (e, listingId) => {
  // do something with listingId
});
```

prefer:

```javascript
// good
$(this).trigger('listingUpdated', { listingId: listing.id });

// ...

$(this).on('listingUpdated', (e, data) => {
  // do something with data.listingId
});
```

⬆ back to top

jQuery

• 26.1 Prefix jQuery object variables with a $. jscs: requireDollarBeforejQueryAssignment

@ZORO EXCEPTION: Ignore.

```javascript
// bad
const sidebar = $('.sidebar');

// good
const $sidebar = $('.sidebar');

// good
const $sidebarBtn = $('.sidebar-btn');
```

• 26.2 Cache jQuery lookups.

  // bad
  function setSidebar() {
    $('.sidebar').hide();
  
    // ...
  
    $('.sidebar').css({
      'background-color': 'pink',
    });
  }
  
  // good
  function setSidebar() {
    const $sidebar = $('.sidebar');
    $sidebar.hide();
  
    // ...
  
    $sidebar.css({
      'background-color': 'pink',
    });
  }

• 26.3 For DOM queries use Cascading $('.sidebar ul') or parent > child $('.sidebar > ul'). jsPerf

• 26.4 Use find with scoped jQuery object queries.

  // bad
  $('ul', '.sidebar').hide();
  
  // bad
  $('.sidebar').find('ul').hide();
  
  // good
  $('.sidebar ul').hide();
  
  // good
  $('.sidebar > ul').hide();
  
  // good
  $sidebar.find('ul').hide();

⬆ back to top

ECMAScript 5 Compatibility

• 27.1 Refer to Kangax’s ES5 compatibility table.

⬆ back to top

ECMAScript 6+ (ES 2015+) Styles

• 28.1 This is a collection of links to the various ES6+ features.

1. Arrow Functions
2. Classes
3. Object Shorthand
4. Object Concise
5. Object Computed Properties
6. Template Strings
7. Destructuring
8. Default Parameters
9. Rest
10. Array Spreads
11. Let and Const
12. Exponentiation Operator
13. Iterators and Generators
14. Modules

• 28.2 Do not use TC39 proposals that have not reached stage 3.

  Why? They are not finalized, and they are subject to change or to be withdrawn entirely. We want to use JavaScript, and proposals are not JavaScript yet.

⬆ back to top

Standard Library

The Standard Library contains utilities that are functionally broken but remain for legacy reasons.

• 29.1 Use Number.isNaN instead of global isNaN. eslint: no-restricted-globals

  Why? The global isNaN coerces non-numbers to numbers, returning true for anything that coerces to NaN. If this behavior is desired, make it explicit.

  // bad
  isNaN('1.2'); // false
  isNaN('1.2.3'); // true
  
  // good
  Number.isNaN('1.2.3'); // false
  Number.isNaN(Number('1.2.3')); // true

• 29.2 Use Number.isFinite instead of global isFinite. eslint: no-restricted-globals

  Why? The global isFinite coerces non-numbers to numbers, returning true for anything that coerces to a finite number. If this behavior is desired, make it explicit.

  // bad
  isFinite('2e3'); // true
  
  // good
  Number.isFinite('2e3'); // false
  Number.isFinite(parseInt('2e3', 10)); // true

⬆ back to top

Testing

• 30.1 Yup.

  function foo() {
    return true;
  }

• 30.2 No, but seriously:
  • Whichever testing framework you use, you should be writing tests!
  • Strive to write many small pure functions, and minimize where mutations occur.
  • Be cautious about stubs and mocks - they can make your tests more brittle.
  • We primarily use mocha at Airbnb. tape is also used occasionally for small, separate modules.
  • 100% test coverage is a good goal to strive for, even if it’s not always practical to reach it.
  • Whenever you fix a bug, write a regression test. A bug fixed without a regression test is almost certainly going to break again in the future.

⬆ back to top

Performance

• On Layout & Web Performance
• String vs Array Concat
• Try/Catch Cost In a Loop
• Bang Function
• jQuery Find vs Context, Selector
• innerHTML vs textContent for script text
• Long String Concatenation
• Are Javascript functions like map(), reduce(), and filter() optimized for traversing arrays?
• Loading...

⬆ back to top

Resources

Learning ES6+

• Latest ECMA spec
• ExploringJS
• ES6 Compatibility Table
• Comprehensive Overview of ES6 Features

Read This

• Standard ECMA-262

Tools

• Code Style Linters
  • ESlint - Airbnb Style .eslintrc
  • JSHint - Airbnb Style .jshintrc
  • JSCS - Airbnb Style Preset (Deprecated, please use ESlint)
• Neutrino preset - neutrino-preset-airbnb-base

Other Style Guides

• Google JavaScript Style Guide
• jQuery Core Style Guidelines
• Principles of Writing Consistent, Idiomatic JavaScript

Other Styles

• Naming this in nested functions - Christian Johansen
• Conditional Callbacks - Ross Allen
• Popular JavaScript Coding Conventions on GitHub - JeongHoon Byun
• Multiple var statements in JavaScript, not superfluous - Ben Alman

Further Reading

• Understanding JavaScript Closures - Angus Croll
• Basic JavaScript for the impatient programmer - Dr. Axel Rauschmayer
• You Might Not Need jQuery - Zack Bloom & Adam Schwartz
• ES6 Features - Luke Hoban
• Frontend Guidelines - Benjamin De Cock

Books

• JavaScript: The Good Parts - Douglas Crockford
• JavaScript Patterns - Stoyan Stefanov
• Pro JavaScript Design Patterns - Ross Harmes and Dustin Diaz
• High Performance Web Sites: Essential Knowledge for Front-End Engineers - Steve Souders
• Maintainable JavaScript - Nicholas C. Zakas
• JavaScript Web Applications - Alex MacCaw
• Pro JavaScript Techniques - John Resig
• Smashing Node.js: JavaScript Everywhere - Guillermo Rauch
• Secrets of the JavaScript Ninja - John Resig and Bear Bibeault
• Human JavaScript - Henrik Joreteg
• Superhero.js - Kim Joar Bekkelund, Mads Mobæk, & Olav Bjorkoy
• JSBooks - Julien Bouquillon
• Third Party JavaScript - Ben Vinegar and Anton Kovalyov
• Effective JavaScript: 68 Specific Ways to Harness the Power of JavaScript - David Herman
• Eloquent JavaScript - Marijn Haverbeke
• You Don’t Know JS: ES6 & Beyond - Kyle Simpson

Blogs

• JavaScript Weekly
• JavaScript, JavaScript...
• Bocoup Weblog
• Adequately Good
• NCZOnline
• Perfection Kills
• Ben Alman
• Dmitry Baranovskiy
• nettuts

Podcasts

• JavaScript Air
• JavaScript Jabber

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In the Wild

This is a list of organizations that are using this style guide. Send us a pull request and we'll add you to the list.

• 123erfasst: 123erfasst/javascript
• 3blades: 3Blades
• 4Catalyzer: 4Catalyzer/javascript
• Aan Zee: AanZee/javascript
• Adult Swim: adult-swim/javascript
• Airbnb: airbnb/javascript
• AltSchool: AltSchool/javascript
• Apartmint: apartmint/javascript
• Ascribe: ascribe/javascript
• Avalara: avalara/javascript
• Avant: avantcredit/javascript
• Axept: axept/javascript
• BashPros: BashPros/javascript
• Billabong: billabong/javascript
• Bisk: bisk
• Bonhomme: bonhommeparis/javascript
• Brainshark: brainshark/javascript
• CaseNine: CaseNine/javascript
• Chartboost: ChartBoost/javascript-style-guide
• ComparaOnline: comparaonline/javascript
• Compass Learning: compasslearning/javascript-style-guide
• DailyMotion: dailymotion/javascript
• DoSomething: DoSomething/eslint-config
• Digitpaint digitpaint/javascript
• Ecosia: ecosia/javascript
• Evernote: evernote/javascript-style-guide
• Evolution Gaming: evolution-gaming/javascript
• EvozonJs: evozonjs/javascript
• ExactTarget: ExactTarget/javascript
• Expensify Expensify/Style-Guide
• Flexberry: Flexberry/javascript-style-guide
• Gawker Media: gawkermedia
• General Electric: GeneralElectric/javascript
• Generation Tux: GenerationTux/javascript
• GoodData: gooddata/gdc-js-style
• Grooveshark: grooveshark/javascript
• Grupo-Abraxas: Grupo-Abraxas/javascript
• Honey: honeyscience/javascript
• How About We: howaboutwe/javascript
• Huballin: huballin
• HubSpot: HubSpot/javascript
• Hyper: hyperoslo/javascript-playbook
• InterCity Group: intercitygroup/javascript-style-guide
• Jam3: Jam3/Javascript-Code-Conventions
• JeopardyBot: kesne/jeopardy-bot
• JSSolutions: JSSolutions/javascript
• Kaplan Komputing: kaplankomputing/javascript
• KickorStick: kickorstick
• Kinetica Solutions: kinetica/javascript
• LEINWAND: LEINWAND/javascript
• Lonely Planet: lonelyplanet/javascript
• M2GEN: M2GEN/javascript
• Mighty Spring: mightyspring/javascript
• MinnPost: MinnPost/javascript
• MitocGroup: MitocGroup/javascript
• ModCloth: modcloth/javascript
• Money Advice Service: moneyadviceservice/javascript
• Muber: muber
• National Geographic: natgeo
• Nimbl3: nimbl3/javascript
• Nulogy: nulogy/javascript
• Orange Hill Development: orangehill/javascript
• Orion Health: orionhealth/javascript
• OutBoxSoft: OutBoxSoft/javascript
• Peerby: Peerby/javascript
• Razorfish: razorfish/javascript-style-guide
• reddit: reddit/styleguide/javascript
• React: facebook.github.io/react/contributing/how-to-contribute.html#style-guide
• REI: reidev/js-style-guide
• Ripple: ripple/javascript-style-guide
• Sainsbury's Supermarkets: jsainsburyplc
• SeekingAlpha: seekingalpha/javascript-style-guide
• Shutterfly: shutterfly/javascript
• Sourcetoad: sourcetoad/javascript
• Springload: springload
• StratoDem Analytics: stratodem/javascript
• SteelKiwi Development: steelkiwi/javascript
• StudentSphere: studentsphere/javascript
• SwoopApp: swoopapp/javascript
• SysGarage: sysgarage/javascript-style-guide
• Syzygy Warsaw: syzygypl/javascript
• Target: target/javascript
• TheLadders: TheLadders/javascript
• The Nerdery: thenerdery/javascript-standards
• T4R Technology: T4R-Technology/javascript
• VoxFeed: VoxFeed/javascript-style-guide
• WeBox Studio: weboxstudio/javascript
• Weggo: Weggo/javascript
• Zillow: zillow/javascript
• ZocDoc: ZocDoc/javascript

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Translation

This style guide is also available in other languages:

• Brazilian Portuguese: armoucar/javascript-style-guide
• Bulgarian: borislavvv/javascript
• Catalan: fpmweb/javascript-style-guide
• Chinese (Simplified): yuche/javascript
• Chinese (Traditional): jigsawye/javascript
• French: nmussy/javascript-style-guide
• German: timofurrer/javascript-style-guide
• Italian: sinkswim/javascript-style-guide
• Japanese: mitsuruog/javascript-style-guide
• Korean: tipjs/javascript-style-guide
• Russian: leonidlebedev/javascript-airbnb
• Spanish: paolocarrasco/javascript-style-guide
• Thai: lvarayut/javascript-style-guide
• Ukrainian: ivanzusko/javascript
• Vietnam: hngiang/javascript-style-guide

The JavaScript Style Guide Guide

• Reference

Chat With Us About JavaScript

• Find us on gitter.

Contributors

• View Contributors

License

(The MIT License)

Copyright (c) 2012 Airbnb

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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Amendments

We encourage you to fork this guide and change the rules to fit your team’s style guide. Below, you may list some amendments to the style guide. This allows you to periodically update your style guide without having to deal with merge conflicts.

};