Airbnb JavaScript Style Guide, Meteor edition

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Airbnb JavaScript Style Guide, Meteor edition

A mostly reasonable approach to JavaScript, with some Meteor flavor

All rules that are automatically linted have the ESLint logo, with a link to the rule, like so:

Types

This section has been eliminated in the Meteor version, because it does not specify any style rules.

References

2.1 Use const for all of your references; avoid using var.

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

```javascript
// bad
var a = 1;
var b = 2;

// good
const a = 1;
const b = 2;
```

2.2 If you must mutate references, use let instead of var.

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

```javascript
// bad
var count = 1;
if (true) {
  count += 1;
}

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

2.3 This section removed in the Meteor edition, because it does not specify any style rules.

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Objects

3.1 Use the literal syntax for object creation.

// bad
const item = new Object();

// good
const item = {};

3.2 and 3.3 eliminated in the Meteor edition because Babel can compile reserved words to work fine in old browsers.

3.4 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.

```javascript

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,
};
```

3.5 Use object method shorthand.

// bad
const atom = {
  value: 1,

  addValue: function (value) {
    return atom.value + value;
  },
};

// good
const atom = {
  value: 1,

  addValue(value) {
    return atom.value + value;
  },
};

3.6 Use property value shorthand.

Why? It is shorter to write and descriptive.

```javascript
const lukeSkywalker = 'Luke Skywalker';

// bad
const obj = {
  lukeSkywalker: lukeSkywalker,
};

// good
const obj = {
  lukeSkywalker,
};
```

3.7 Group your shorthand properties at the beginning of your object declaration.

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

```javascript
const anakinSkywalker = 'Anakin Skywalker';
const lukeSkywalker = 'Luke Skywalker';

// bad
const obj = {
  episodeOne: 1,
  twoJedisWalkIntoACantina: 2,
  lukeSkywalker,
  episodeThree: 3,
  mayTheFourth: 4,
  anakinSkywalker,
};

// good
const obj = {
  lukeSkywalker,
  anakinSkywalker,
  episodeOne: 1,
  twoJedisWalkIntoACantina: 2,
  episodeThree: 3,
  mayTheFourth: 4,
};
```

3.8 Use object spreads ... to copy objects.

// bad
const copy = {};
Object.keys(obj).forEach((key) => {
  copy[key] = obj[key];
});

// bad
const copy = {};
for (var key in obj) {
  if (Object.prototype.hasOwnProperty.call(obj, key)) {
    copy[key] = obj[key];
  }
}

// good
const copy = { ...obj };

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Arrays

4.1 Use the literal syntax for array creation.

// 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++) {
  itemsCopy[i] = items[i];
}

// good
const itemsCopy = [...items];

4.4 To convert an array-like object to an array, use Array#from.

const foo = document.querySelectorAll('.foo');
const nodes = Array.from(foo);

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Destructuring

5.1 Use object destructuring when accessing and using multiple properties of an object.

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

```javascript
// bad
function getFullName(user) {
  const firstName = user.firstName;
  const lastName = user.lastName;

  return `${firstName} ${lastName}`;
}

// good
function getFullName(obj) {
  const { firstName, lastName } = obj;
  return `${firstName} ${lastName}`;
}

// best
function getFullName({ firstName, lastName }) {
  return `${firstName} ${lastName}`;
}
```

5.2 Use array destructuring.

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.

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, right } = processInput(input);
```

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Strings

6.1 Use single quotes '' for strings.

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

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

6.2 Single-line strings longer than 80 characters should be written across multiple lines using string concatenation. If you are writing a multiline string, use template strings as in 6.4. This is a change in the Meteor edition. Note: If overused, long strings with concatenation could impact performance. jsPerf & Discussion.

// 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 This non-rule merged as a note into the previous rule in the Meteor edition.

6.4 When programmatically building up strings, use template strings instead of concatenation.

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

```javascript
// bad
function sayHi(name) {
  return 'How are you, ' + name + '?';
}

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

// good
function sayHi(name) {
  return `How are you, ${name}?`;
}
```

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Functions

7.1 Use function declarations instead of function expressions.

Why? Function declarations are named, so they're easier to identify in call stacks. Also, the whole body of a function declaration is hoisted, whereas only the reference of a function expression is hoisted. This rule makes it possible to always use Arrow Functions in place of function expressions.

```javascript
// bad
const foo = function () {
};

// good
function foo() {
}
```

7.2 Removed in the Meteor edition.
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. 7.4 Note: ECMA-262 defines a block as a list of statements. A function declaration is not a statement. Read ECMA-262's note on this issue. This note merged into the previous rule in the Meteor edition.
```
// 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 nope(name, options, arguments) {
  // ...stuff...
}

// good
function yup(name, options, args) {
  // ...stuff...
}

7.6 Never use arguments, opt to use rest syntax ... instead.

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

```javascript
// 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 Use argument spreads to interpolate arguments in function calls.

const prefix = [a, b];
const suffix = [c, d, e];

// bad
prefix.push.apply(prefix, suffix);

// good
prefix.push(...suffix);

// bad
someFunction.apply(null, prefix.concat(suffix));

// good
someFunction(...prefix, ...suffix);

The exception to this advice is when you really need to use a different, non-null value of this. Then .apply (or .call) is probably a better option.

The same goes for new expressions.

class A {
  constructor(...args) { ... }
}

// really bad
const instance = Object.create(A.prototype);
A.prototype.constructor.apply(instance, prefix.concat(suffix));

// good
const instance = new A(...prefix, ...suffix);

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Arrow Functions

8.1 When you must use function expressions (as when passing an anonymous function), use arrow function notation.

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 function declaration.

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

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

8.2 If the function body fits on one line and there is only a single argument, feel free to omit the braces and parentheses, and use the implicit return. Otherwise, add the parentheses, braces, and use a return statement.

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

Why not? If you plan on returning an object.

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

// good
[1, 2, 3].reduce((total, n) => {
  return total + n;
}, 0);
```

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Constructors

9.1 Always use class. Avoid manipulating prototype directly.

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.

```javascript
// 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 {
  contructor(options = {}) {
    this.name = options.name || 'no name';
  }

  getName() {
    return this.name;
  }

  toString() {
    return `Jedi - ${this.getName()}`;
  }
}

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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.

```javascript
// 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.

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.

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;
```

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Iterators and Generators

11.1 Don't use iterators. Prefer JavaScript's higher-order functions like map() and reduce() instead of loops like for-of.

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

```javascript
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;
```

11.2 Don't use generators for now.

Why? They don't transpile well to ES5.

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Properties

12.1 Use dot notation when accessing properties.

const luke = {
  jedi: true,
  age: 28,
};

// bad
const isJedi = luke['jedi'];

// good
const isJedi = luke.jedi;

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

const luke = {
  jedi: true,
  age: 28,
};

function getProp(prop) {
  return luke[prop];
}

const isJedi = getProp('jedi');

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Variables

13.1 Always use const 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.
```
// bad
superPower = new SuperPower();

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

13.2 Use one const declaration per variable.

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.

// 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.

```javascript
// 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.

```javascript
// good
function() {
  test();
  console.log('doing stuff..');

  //..other stuff..

  const name = getName();

  if (name === 'test') {
    return false;
  }

  return name;
}

// bad - unnessary function call
function(hasName) {
  const name = getName();

  if (!hasName) {
    return false;
  }

  this.setFirstName(name);

  return true;
}

// good
function(hasName) {
  if (!hasName) {
    return false;
  }

  const name = getName();
  this.setFirstName(name);

  return true;
}
```

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Hoisting

14.1 14.2 14.3 14.4 Non-rules removed in the Meteor edition.
For more information refer to [JavaScript Scoping & Hoisting](http://www.adequatelygood.com/2010/2/JavaS cript-Scoping-and-Hoisting) by Ben Cherry.

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Comparison Operators & Equality

15.1 Use === and !== over == and !=.
15.2 /15.3 /15.4 Use shortcuts. Note: Conditional statements such as the if statement evaluate their expression using coercion with the ToBoolean abstract method and always follow the simple rules below. For more information see Truth Equality and JavaScript by Angus Croll. (15.2, 15.3, and 15.4 merged in Meteor edition):
- 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
```
// bad
if (name !== '') {
  // ...stuff...
}

// good
if (name) {
  // ...stuff...
}

// bad
if (collection.length > 0) {
  // ...stuff...
}

// good
if (collection.length) {
  // ...stuff...
}

// note
if ([0]) {
  // true
  // An array is an object, objects evaluate to true
}
```

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Blocks

16.1 Use braces with all multi-line blocks.

// bad
if (test)
  return false;

// good
if (test) return false;

// good
if (test) {
  return false;
}

// bad
function() { return false; }

// good
function() {
  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.

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

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

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Comments

17.1 Use /** ... */ for method doc comments. Include a description, specify types and values for all parameters and return values. In the Meteor edition, this rule has been updated to only refer to doc comments.

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

  // ...stuff...

  return element;
}

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

  // ...stuff...

  return element;
}

17.2 Use // for all other comments. Place single line comments on a newline above the subject of the comment. Put an empty line before the comment. Has been updated in Meteor edition to refer to all non-doc comments.

// 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;
}

17.3 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.

17.4 Use // FIXME: to annotate problems.

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

17.5 Use // TODO: to annotate solutions to problems.

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

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Whitespace

18.1 Use soft tabs set to 2 spaces.

// bad
function() {
∙∙∙∙const name;
}

// bad
function() {
∙const name;
}

// good
function() {
∙∙const name;
}

18.2 Place 1 space before the leading brace.

// 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',
});

18.3 Place 1 space before the opening parenthesis in control statements (if, while etc.). Place no space before the argument list in function calls and declarations.

// bad
if(isJedi) {
  fight ();
}

// good
if (isJedi) {
  fight();
}

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

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

18.4 Set off operators with spaces.

// bad
const x=y+5;

// good
const x = y + 5;

18.5 End files with a single newline character.

// bad
(function(global) {
  // ...stuff...
})(this);

// bad
(function(global) {
  // ...stuff...
})(this);↵
↵

// good
(function(global) {
  // ...stuff...
})(this);↵

18.5 Use indentation when making long method chains. Use a leading dot, which emphasizes that the line is a method call, not a new statement.

// 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').class('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);

18.6 Leave a blank line after blocks and before the next statement.

// 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;

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Commas

19.1 Leading commas: Nope.

// 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',
};

19.2 Additional trailing comma: Yup.

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.

```javascript
// bad - git diff without trailing comma
const hero = {
     firstName: 'Florence',
-    lastName: 'Nightingale'
+    lastName: 'Nightingale',
+    inventorOf: ['coxcomb graph', 'mordern nursing']
}

// good - git diff with trailing comma
const hero = {
     firstName: 'Florence',
     lastName: 'Nightingale',
+    inventorOf: ['coxcomb chart', 'mordern nursing'],
}

// bad
const hero = {
  firstName: 'Dana',
  lastName: 'Scully'
};

const heroes = [
  'Batman',
  'Superman'
];

// good
const hero = {
  firstName: 'Dana',
  lastName: 'Scully',
};

const heroes = [
  'Batman',
  'Superman',
];
```

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Semicolons

20.1 Yup.

// bad
(function() {
  const name = 'Skywalker'
  return name
})()

// good
(() => {
  const name = 'Skywalker';
  return name;
})();

// good (guards against the function becoming an argument when two files with IIFEs are concatenated)
;(() => {
  const name = 'Skywalker';
  return name;
})();

Type Casting & Coercion

21.1 Perform type coercion at the beginning of the statement.

21.2 Strings:

//  => this.reviewScore = 9;

// bad
const totalScore = this.reviewScore + '';

// good
const totalScore = String(this.reviewScore);

21.3 Use parseInt to convert strings to numbers, and always with a radix argument.
```
const inputValue = '4';

// bad
const val = new Number(inputValue);

// bad
const val = inputValue >> 0;

// bad
const val = parseInt(inputValue);

// good
const val = parseInt(inputValue, 10);
```
Use the Number constructor (without new) to coerce values that are not strings to numbers, as in Number(new Date) + 1000. The unary + operator is an acceptable shorthand for Number(...), but only if the expression is not involved in a larger expression, as in +new Date.

Note that the Number constructor will return NaN if the value cannot be converted to a number, including when the value is undefined. If the output might be NaN (likely because the input might be undefined), be sure to test for that possibility after attempting the conversion:
```
let val = Number(inputValue);
if (isNaN(val)) {
  val = 0;
}
```
Better yet, avoid the possibility of NaN through other means, such as providing default values for optional function parameters.

21.4 If you have a very good reason for using some other kind of coercion technique, be it for performance or because you need a very specific output behavior, then you should absolutely leave a comment justifying your choice.

// 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;

// good
// Truthy inputs must always be coerced to 1, and falsy inputs must
// always be cocerced to 0.
const zeroOrOne = inputValue ? 1 : 0;

21.5 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
```

21.6 Booleans:

const age = 0;

// bad
const hasAge = new Boolean(age);

// good
const hasAge = Boolean(age);

// good
const hasAge = !!age;

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Naming Conventions

22.1 Avoid single letter names. Be descriptive with your naming.

// bad
function q() {
  // ...stuff...
}

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

22.2 Use camelCase when naming objects, functions, and instances.

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

// good
const thisIsMyObject = {};
function thisIsMyFunction() {}

22.3 Use PascalCase when naming constructors or classes.

// 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',
});

22.4 Use a leading underscore _ when naming private properties.

// bad
this.__firstName__ = 'Panda';
this.firstName_ = 'Panda';

// good
this._firstName = 'Panda';

22.5 Don't save references to this. Use arrow functions or Function#bind.

// 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);
  };
}

22.6 If your file exports a single class, your filename should be exactly the name of the class.

// file contents
export default class CheckBox {
  // ...
}

// in some other file
// bad
import CheckBox from './checkBox';

// bad
import CheckBox from './check_box';

// good
import CheckBox from './CheckBox';

22.7 Use camelCase when you export-default a function. Your filename should be identical to your function's name.
```
function makeStyleGuide() {
}

export default makeStyleGuide;
```

22.8 Use PascalCase when you export a singleton / function library / bare object.

const AirbnbStyleGuide = {
  es6: {
  }
};

export default AirbnbStyleGuide;

22.9 Prefer exporting declarations where they are declared, rather than at the end of the file:

// bad
function createUser(name) { ... }
function getOrCreateUser(name) { ... }
// ... rest of file ...
export {
  createUser,
  getOrCreateUser,
}

// good
export function createUser(name) { ... }
export function getOrCreateUser(name) { ... }
// ... rest of file ...

This style ensures that the set of exports remains up-to-date as declarations are added or removed.

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Accessors

23.1 Accessor functions for properties are not required.

23.2 If you do make accessor functions use getVal() and setVal('hello').

// bad
dragon.age();

// good
dragon.getAge();

// bad
dragon.age(25);

// good
dragon.setAge(25);

23.3 If the property is a boolean, use isVal() or hasVal().

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

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

23.4 It's okay to create get() and set() functions, but be consistent.

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

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

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

23.5 Strongly prefer accessor methods to defining ES5 getter and setter properties:

class Jedi {
  constructor({ lightsaber = blue }) {
    this._lightsaber = lightsaber;
  }

  // bad; use a normal getter method instead
  get lightsaber() {
    return this._lightsaber;
  }

  // bad; use a normal setter method instead
  set lightsaber(newLightSaber) {
    return this._lightsaber = newLightSaber;
  }
}

Not only is this style rarely more readable than the method equivalent, performance can suffer dramatically when code relies on specially-defined properties rather than just using normal properties.

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Events

24.1 When attaching data payloads to events (whether DOM events or something more proprietary like Backbone events), pass 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:

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

...

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

prefer:

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

...

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

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jQuery

25.1 Prefix jQuery object variables with a $.

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

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

25.2 Cache jQuery lookups.

// bad
function setSidebar() {
  $('.sidebar').hide();

  // ...stuff...

  $('.sidebar').css({
    'background-color': 'pink'
  });
}

// good
function setSidebar() {
  const $sidebar = $('.sidebar');
  $sidebar.hide();

  // ...stuff...

  $sidebar.css({
    'background-color': 'pink'
  });
}

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

25.4 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();

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ECMAScript 5 Compatibility

26.1 Refer to Kangax's ES5 compatibility table.

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ECMAScript 6 Styles

27.1 This is a collection of links to the various es6 features.

Arrow Functions
Classes
Object Shorthand
Object Concise
Object Computed Properties
Template Strings
Destructuring
Default Parameters
Rest
Array Spreads
Let and Const
Iterators and Generators
Modules

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Contributors

View Contributors

License

(The MIT License)

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.

⬆ back to top

Name		Name	Last commit message	Last commit date
Latest commit History 480 Commits
es5		es5
linters		linters
packages/eslint-config-airbnb		packages/eslint-config-airbnb
react		react
.gitignore		.gitignore
README.md		README.md
package.json		package.json

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Airbnb JavaScript Style Guide, Meteor edition

Table of Contents

Types

References

Objects

Arrays

Destructuring

Strings

Functions

Arrow Functions

Constructors

Modules

Iterators and Generators

Properties

Variables

Hoisting

Comparison Operators & Equality

Blocks

Comments

Whitespace

Commas

Semicolons

Type Casting & Coercion

Naming Conventions

Accessors

Events

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Contributors

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Airbnb JavaScript Style Guide, Meteor edition

Table of Contents

Types

References

Objects

Arrays

Destructuring

Strings

Functions

Arrow Functions

Constructors

Modules

Iterators and Generators

Properties

Variables

Hoisting

Comparison Operators & Equality

Blocks

Comments

Whitespace

Commas

Semicolons

Type Casting & Coercion

Naming Conventions

Accessors

Events

jQuery

ECMAScript 5 Compatibility

ECMAScript 6 Styles

Contributors

License

};

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