mofo-style - npm Package Compare versions

Comparing version 1.0.1 to 1.1.0

.npmignore

package.json

		{
		"name": "mofo-style",
		"version": "1.0.1",
		"version": "1.1.0",
		"description": "A Javascript style guide including linters for the Mozilla Foundation Engineering team.",
		@@ -5,0 +5,0 @@ "main": "",

1529

README.md

		@@ -1,1527 +0,22 @@
		# Mozilla Foundation JavaScript Style Guide() {
		# Mozilla Foundation JS Style Guide

		Originally forked from the Airbnb style guide -- a mostly reasonable approach to JavaScript
		This repo contains "RC" files, which represent our standard rules, for several different JavaScript linters ([JSHint](http://jshint.com/), [JSCS](http://jscs.info/), and [JSBeautifier](https://github.com/beautify-web/js-beautify)).

		In your project you can use npm to install the RC files as a module, which can then be individually used by your project's build system (eg: Gulp or Grunt). Most linting tasks/plugins allow you to specify an external RC file, which you can point to your copies in `node_modules`.

		## Table of Contents
		Simply run `npm install mofo-style --save-dev`.

		1. [Types](#types)
		1. [undefined](#undefined)
		1. [Objects](#objects)
		1. [Arrays](#arrays)
		1. [Strings](#strings)
		1. [Functions](#functions)
		1. [Properties](#properties)
		1. [Variables](#variables)
		1. [Hoisting](#hoisting)
		1. [Conditional Expressions & Equality](#conditional-expressions--equality)
		1. [Blocks](#blocks)
		1. [Comments](#comments)
		1. [Whitespace](#whitespace)
		1. [Commas](#commas)
		1. [Semicolons](#semicolons)
		1. [Type Casting & Coercion](#type-casting--coercion)
		1. [Naming Conventions](#naming-conventions)
		1. [Accessors](#accessors)
		1. [Constructors](#constructors)
		1. [Events](#events)
		1. [Modules](#modules)
		1. [jQuery](#jquery)
		1. [ECMAScript 5 Compatibility](#ecmascript-5-compatibility)
		1. [Testing](#testing)
		1. [Performance](#performance)
		1. [Resources](#resources)
		1. [In the Wild](#in-the-wild)
		1. [Translation](#translation)
		1. [The JavaScript Style Guide Guide](#the-javascript-style-guide-guide)
		1. [Contributors](#contributors)
		1. [License](#license)
		## Task Naming

		## Types
		You should have at least 2 style tasks in your runner.

		- Primitives: When you access a primitive type you work directly on its value
		- `validate` - Run all 3 linters in read only mode and report any errors.
		- `clean` - Run all 3 linters but also run JSBeautifier in write mode to automatically fix any formatting errors that it's capable of repairing.

		+ `string`
		+ `number`
		+ `boolean`
		+ `null`
		+ `undefined`
		## Rules

		```javascript
		var foo = 1;
		var bar = foo;
		Refer to the [RC files](https://github.com/MozillaFoundation/javascript-style-guide/tree/master/linters) for specifics.

		bar = 9;
		### Roadmap

		console.log(foo, bar); // => 1, 9
		```
		- Complex: When you access a complex type you work on a reference to its value.

		+ `object`
		+ `array`
		+ `function`

		```javascript
		var foo = [1, 2];
		var bar = foo;

		bar[0] = 9;

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

		[⬆ back to top](#table-of-contents)

		## undefined

		- `undefined` is an object. You should use it as an object. You can test for it. For instance:

		```javascript
		// good
		function pow(a, b) {
		if (b === undefined) {
		b = 1;
		}
		return Math.pow(a, b);
		}

		// bad
		function pow(a, b) {
		if (typeof b == "undefined") {
		b = 1;
		}
		return Math.pow(a, b);
		}
		```

		- Only use `typeof x == "undefined"` when the variable (`x`) may not be declared, and it would be an error to test `x === undefined`:

		```javascript
		if (typeof Module == "undefined") {
		Module = {};
		}

		// But also okay, for browser-only code:
		if (window.Module === undefined) {
		Module = {};
		}
		```

		Note that you can't use `window` in Node.js; if you think your code could be used in a server context you should use the first form.

		[⬆ back to top](#table-of-contents)

		## Objects

		- Use the literal syntax for object creation.

		```javascript
		// bad
		var item = new Object();

		// good
		var item = {};
		```


		```javascript
		if (typeof Module == "undefined") {
		Module = {};
		}

		// But also okay, for browser-only code:
		if (window.Module === undefined) {
		Module = {};
		}
		```

		Note that you can't use `window` in Node.js; if you think your code could be used in a server context you should use the first form.

		[⬆ back to top](#table-of-contents)

		## Objects

		- Use the literal syntax for object creation.

		```javascript
		// bad
		var item = new Object();

		// good
		var item = {};
		```

		- You may use [reserved words](https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Reserved_Words) as keys.

		As an example that reserved words are both okay right now and will be indefinitely, the [IndexedDB API](https://developer.mozilla.org/en-US/docs/IndexedDB/Using_IndexedDB) uses `cursor.continue()`


		[⬆ back to top](#table-of-contents)

		## Arrays

		- Use the literal syntax for array creation

		```javascript
		// bad
		var items = new Array();

		// good
		var items = [];
		```

		- If you don't know array length use Array#push.

		```javascript
		var someStack = [];


		// bad
		someStack[someStack.length] = 'abracadabra';

		// good
		someStack.push('abracadabra');
		```

		- When you need to copy an array use Array#slice. [jsPerf](http://jsperf.com/converting-arguments-to-an-array/7)

		```javascript
		var len = items.length;
		var itemsCopy = [];
		var i;

		// bad
		for (i = 0; i < len; i++) {
		itemsCopy[i] = items[i];
		}

		// good
		itemsCopy = items.slice();
		```

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

		```javascript
		function trigger() {
		var args = Array.prototype.slice.call(arguments);
		...
		}
		```

		[⬆ back to top](#table-of-contents)


		## Strings

		- Use single or double quotes (`'` or `"`) for strings. There is a slight preference for double-quotes, aligning with Mozilla style.

		- Strings longer than 80 characters should be written across multiple lines using string concatenation.

		- Note: If overused, long strings with concatenation could impact performance. [jsPerf](http://jsperf.com/ya-string-concat) & [Discussion](https://github.com/airbnb/javascript/issues/40)

		```javascript
		// bad
		var 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
		var 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
		var 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.';
		```

		- When programmatically building up a string, use Array#join instead of string concatenation. Mostly for IE: [jsPerf](http://jsperf.com/string-vs-array-concat/2).

		```javascript
		var items;
		var messages;
		var length;
		var i;

		messages = [{
		state: 'success',
		message: 'This one worked.'
		}, {
		state: 'success',
		message: 'This one worked as well.'
		}, {
		state: 'error',
		message: 'This one did not work.'
		}];

		length = messages.length;

		// bad
		function inbox(messages) {
		items = '<ul>';

		for (i = 0; i < length; i++) {
		items += '<li>' + messages[i].message + '</li>';
		}

		return items + '</ul>';
		}

		// good
		function inbox(messages) {
		items = [];

		for (i = 0; i < length; i++) {
		items[i] = messages[i].message;
		}

		return '<ul><li>' + items.join('</li><li>') + '</li></ul>';
		}
		```

		[⬆ back to top](#table-of-contents)


		## Functions

		- Function expressions:

		```javascript
		// anonymous function expression
		var anonymous = function() {
		return true;
		};

		// named function expression
		var named = function named() {
		return true;
		};

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

		- 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.
		- 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](http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf#page=97).

		```javascript
		// bad
		if (currentUser) {
		function test() {
		console.log('Nope.');
		}
		}

		// good
		var test;
		if (currentUser) {
		test = function test() {
		console.log('Yup.');
		};
		}
		```

		- Never name a parameter `arguments`, this will take precedence over the `arguments` object that is given to every function scope.

		```javascript
		// bad
		function nope(name, options, arguments) {
		// ...stuff...
		}

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

		[⬆ back to top](#table-of-contents)



		## Properties

		- Use dot notation when accessing properties.

		```javascript
		var luke = {
		jedi: true,
		age: 28
		};

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

		// good
		var isJedi = luke.jedi;
		```

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

		```javascript
		var luke = {
		jedi: true,
		age: 28
		};

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

		var isJedi = getProp('jedi');
		```

		[⬆ back to top](#table-of-contents)


		## Variables

		- Always use `var` 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.

		```javascript
		// bad
		superPower = new SuperPower();

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

		- Use one `var` declaration per variable and declare each variable on a newline.

		```javascript
		// bad
		var items = getItems(),
		goSportsTeam = true,
		dragonball = 'z';

		// good
		var items = getItems();
		var goSportsTeam = true;
		var dragonball = 'z';
		```

		- Assign variables at the top of their scope. This helps avoid issues with variable declaration and assignment hoisting related issues.

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

		//..other stuff..

		var name = getName();

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

		return name;
		}

		// good
		function() {
		var name = getName();

		test();
		console.log('doing stuff..');

		//..other stuff..

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

		return name;
		}

		// bad
		function() {
		var name = getName();

		if (!arguments.length) {
		return false;
		}

		return true;
		}

		// good
		function() {
		if (!arguments.length) {
		return false;
		}

		var name = getName();

		return true;
		}
		```

		- As an exception, declaring a variable in a `for` loop is common and okay.

		```javascript
		// ok
		for (var i=0; i<array.length; i++) {
		...
		}
		```


		[⬆ back to top](#table-of-contents)


		## Hoisting

		- Variable declarations get hoisted to the top of their scope, their assignment does not.

		```javascript
		// 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() {
		var declaredButNotAssigned;
		console.log(declaredButNotAssigned); // => undefined
		declaredButNotAssigned = true;
		}
		```

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

		```javascript
		function example() {
		console.log(anonymous); // => undefined

		anonymous(); // => TypeError anonymous is not a function

		var anonymous = function() {
		console.log('anonymous function expression');
		};
		}
		```

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

		```javascript
		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');
		}
		}
		```

		- Function declarations hoist their name and the function body.

		```javascript
		function example() {
		superPower(); // => Flying

		function superPower() {
		console.log('Flying');
		}
		}
		```

		- For more information refer to [JavaScript Scoping & Hoisting](http://www.adequatelygood.com/2010/2/JavaScript-Scoping-and-Hoisting) by [Ben Cherry](http://www.adequatelygood.com/)

		[⬆ back to top](#table-of-contents)



		## Conditional Expressions & Equality

		- Use `===` and `!==` over `==` and `!=`.
		- Conditional expressions are evaluated using coercion with the `ToBoolean` 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

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

		- Use shortcuts.

		```javascript
		// bad
		if (name !== '') {
		// ...stuff...
		}

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

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

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

		- For more information see [Truth Equality and JavaScript](http://javascriptweblog.wordpress.com/2011/02/07/truth-equality-and-javascript/#more-2108) by Angus Croll

		[⬆ back to top](#table-of-contents)


		## Blocks

		- Use braces with all multi-line blocks.

		```javascript
		// bad
		if (test)
		return false;

		// good
		if (test) return false;

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

		// bad
		function() { return false; }

		// good
		function() {
		return false;
		}
		```

		[⬆ back to top](#table-of-contents)


		## Comments

		- Use `/** ... */` for multiline comments. Include a description, specify types and values for all parameters and return values.

		```javascript
		// 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;
		}
		```

		- 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.

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

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

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

		return type;
		}

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

		// set the default type to 'no type'
		var type = this._type \|\| 'no type';

		return type;
		}
		```

		- 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`.

		- Use `// FIXME:` to annotate problems

		```javascript
		function Calculator() {

		// FIXME: shouldn't use a global here
		total = 0;

		return this;
		}
		```

		- Use `// TODO:` to annotate solutions to problems

		```javascript
		function Calculator() {

		// TODO: total should be configurable by an options param
		this.total = 0;

		return this;
		}
		```

		[⬆ back to top](#table-of-contents)


		## Whitespace

		- Use soft tabs set to 2 spaces

		```javascript
		// bad
		function() {
		∙∙∙∙var name;
		}

		// bad
		function() {
		∙var name;
		}

		// good
		function() {
		∙∙var name;
		}
		```

		- Place 1 space before the leading brace.

		```javascript
		// 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'
		});
		```

		- Set off operators with spaces.

		```javascript
		// bad
		var x=y+5;

		// good
		var x = y + 5;
		```

		- End files with a single newline character.

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

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

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

		- Use indentation when making long method chains.

		```javascript
		// bad
		$('#items').find('.selected').highlight().end().find('.open').updateCount();

		// good
		$('#items')
		.find('.selected')
		.highlight()
		.end()
		.find('.open')
		.updateCount();

		// bad
		var 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
		var 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);
		```

		[⬆ back to top](#table-of-contents)

		## Commas

		- Leading commas: Nope.

		```javascript
		// bad
		var hero = {
		firstName: 'Bob'
		, lastName: 'Parr'
		, heroName: 'Mr. Incredible'
		, superPower: 'strength'
		};

		// good
		var hero = {
		firstName: 'Bob',
		lastName: 'Parr',
		heroName: 'Mr. Incredible',
		superPower: 'strength'
		};
		```

		- Additional trailing comma: Nope. This can cause problems with IE6/7 and IE9 if it's in quirksmode. Also, in some implementations of ES3 would add length to an array if it had an additional trailing comma. This was clarified in ES5 ([source](http://es5.github.io/#D)):

		> Edition 5 clarifies the fact that a trailing comma at the end of an ArrayInitialiser does not add to the length of the array. This is not a semantic change from Edition 3 but some implementations may have previously misinterpreted this.

		```javascript
		// bad
		var hero = {
		firstName: 'Kevin',
		lastName: 'Flynn',
		};

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

		// good
		var hero = {
		firstName: 'Kevin',
		lastName: 'Flynn'
		};

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

		[⬆ back to top](#table-of-contents)


		## Semicolons

		- Yup.

		```javascript
		// bad
		(function() {
		var name = 'Skywalker'
		return name
		})()

		// good
		(function() {
		var name = 'Skywalker';
		return name;
		})();

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

		[Read more](http://stackoverflow.com/a/7365214/1712802).

		[⬆ back to top](#table-of-contents)


		## Type Casting & Coercion

		- Perform type coercion at the beginning of the statement.
		- Strings:

		```javascript
		// => this.reviewScore = 9;

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

		// good
		var totalScore = '' + this.reviewScore;

		// bad
		var totalScore = '' + this.reviewScore + ' total score';

		// good
		var totalScore = this.reviewScore + ' total score';
		```

		- Use `parseInt` for Numbers and always with a radix for type casting.

		```javascript
		var inputValue = '4';

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

		// bad
		var val = +inputValue;

		// bad
		var val = inputValue >> 0;

		// bad
		var val = parseInt(inputValue);

		// good
		var val = Number(inputValue);

		// good
		var val = parseInt(inputValue, 10);
		```

		- If for whatever reason you are doing something wild and `parseInt` is your bottleneck and need to use Bitshift for [performance reasons](http://jsperf.com/coercion-vs-casting/3), leave a comment explaining why and what you're doing.

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

		- Note: Be careful when using bitshift operations. Numbers are represented as [64-bit values](http://es5.github.io/#x4.3.19), but Bitshift operations always return a 32-bit integer ([source](http://es5.github.io/#x11.7)). Bitshift can lead to unexpected behavior for integer values larger than 32 bits. [Discussion](https://github.com/airbnb/javascript/issues/109). Largest signed 32-bit Int is 2,147,483,647:

		```javascript
		2147483647 >> 0 //=> 2147483647
		2147483648 >> 0 //=> -2147483648
		2147483649 >> 0 //=> -2147483647
		```

		- Booleans:

		```javascript
		var age = 0;

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

		// good
		var hasAge = Boolean(age);

		// good
		var hasAge = !!age;
		```

		[⬆ back to top](#table-of-contents)


		## Naming Conventions

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

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

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

		- Use camelCase when naming objects, functions, and instances

		```javascript
		// bad
		var OBJEcttsssss = {};
		var this_is_my_object = {};
		function c() {}
		var u = new user({
		name: 'Bob Parr'
		});

		// good
		var thisIsMyObject = {};
		function thisIsMyFunction() {}
		var user = new User({
		name: 'Bob Parr'
		});
		```

		- Use PascalCase when naming constructors or classes

		```javascript
		// bad
		function user(options) {
		this.name = options.name;
		}

		var bad = new user({
		name: 'nope'
		});

		// good
		function User(options) {
		this.name = options.name;
		}

		var good = new User({
		name: 'yup'
		});
		```


		- When saving a reference to `this` use `self`.

		```javascript
		// bad
		function() {
		var _this = this;
		return function() {
		console.log(_this);
		};
		}

		// good
		function() {
		var self = this;
		return function() {
		console.log(self);
		};
		}
		```

		- Name your functions. This is helpful for stack traces.

		```javascript
		// bad
		var log = function(msg) {
		console.log(msg);
		};

		// good
		var log = function log(msg) {
		console.log(msg);
		};
		```

		- Note: IE8 and below exhibit some quirks with named function expressions. See [http://kangax.github.io/nfe/](http://kangax.github.io/nfe/) for more info.

		[⬆ back to top](#table-of-contents)


		## Accessors

		- Accessor functions for properties are not required
		- If the property is a boolean, use isVal() or hasVal()

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

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

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

		```javascript
		function Jedi(options) {
		options \|\| (options = {});
		var lightsaber = options.lightsaber \|\| 'blue';
		this.set('lightsaber', lightsaber);
		}

		Jedi.prototype.set = function(key, val) {
		this[key] = val;
		};

		Jedi.prototype.get = function(key) {
		return this[key];
		};
		```

		[⬆ back to top](#table-of-contents)


		## Constructors

		- Assign methods to the prototype object, instead of overwriting the prototype with a new object. Overwriting the prototype makes inheritance impossible: by resetting the prototype you'll overwrite the base!

		```javascript
		function Jedi() {
		console.log('new jedi');
		}

		// bad
		Jedi.prototype = {
		fight: function fight() {
		console.log('fighting');
		},

		block: function block() {
		console.log('blocking');
		}
		};

		// good
		Jedi.prototype.fight = function fight() {
		console.log('fighting');
		};

		Jedi.prototype.block = function block() {
		console.log('blocking');
		};
		```

		- Methods can return `this` to help with method chaining.

		```javascript
		// bad
		Jedi.prototype.jump = function() {
		this.jumping = true;
		return true;
		};

		Jedi.prototype.setHeight = function(height) {
		this.height = height;
		};

		var luke = new Jedi();
		luke.jump(); // => true
		luke.setHeight(20); // => undefined

		// good
		Jedi.prototype.jump = function() {
		this.jumping = true;
		return this;
		};

		Jedi.prototype.setHeight = function(height) {
		this.height = height;
		return this;
		};

		var luke = new Jedi();

		luke.jump()
		.setHeight(20);
		```


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

		```javascript
		function Jedi(options) {
		options \|\| (options = {});
		this.name = options.name \|\| 'no name';
		}

		Jedi.prototype.getName = function getName() {
		return this.name;
		};

		Jedi.prototype.toString = function toString() {
		return 'Jedi - ' + this.getName();
		};
		```

		[⬆ back to top](#table-of-contents)


		## Events

		- 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:

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

		...

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

		prefer:

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

		...

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

		[⬆ back to top](#table-of-contents)


		## Modules

		- The module should start with a `!`. This ensures that if a malformed module forgets to include a final semicolon there aren't errors in production when the scripts get concatenated. [Explanation](https://github.com/airbnb/javascript/issues/44#issuecomment-13063933)
		- The file should be named with camelCase, live in a folder with the same name, and match the name of the single export.
		- Add a method called `noConflict()` that sets the exported module to the previous version and returns this one.
		- Always declare `'use strict';` at the top of the module.

		```javascript
		// fancyInput/fancyInput.js

		!function(global) {
		'use strict';

		var previousFancyInput = global.FancyInput;

		function FancyInput(options) {
		this.options = options \|\| {};
		}

		FancyInput.noConflict = function noConflict() {
		global.FancyInput = previousFancyInput;
		return FancyInput;
		};

		global.FancyInput = FancyInput;
		}(this);
		```

		[⬆ back to top](#table-of-contents)


		## jQuery

		- Cache jQuery lookups.

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

		// ...stuff...

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

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

		// ...stuff...

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

		- For DOM queries use Cascading `$('.sidebar ul')` or parent > child `$('.sidebar > ul')`. [jsPerf](http://jsperf.com/jquery-find-vs-context-sel/16)
		- Use `find` with scoped jQuery object queries.

		```javascript
		// 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](#table-of-contents)


		## ECMAScript 5 Compatibility

		- Refer to [Kangax](https://twitter.com/kangax/)'s ES5 [compatibility table](http://kangax.github.com/es5-compat-table/)

		[⬆ back to top](#table-of-contents)


		## Testing

		- Yup.

		```javascript
		function() {
		return true;
		}
		```

		[⬆ back to top](#table-of-contents)


		## Performance

		- [On Layout & Web Performance](http://kellegous.com/j/2013/01/26/layout-performance/)
		- [String vs Array Concat](http://jsperf.com/string-vs-array-concat/2)
		- [Try/Catch Cost In a Loop](http://jsperf.com/try-catch-in-loop-cost)
		- [Bang Function](http://jsperf.com/bang-function)
		- [jQuery Find vs Context, Selector](http://jsperf.com/jquery-find-vs-context-sel/13)
		- [innerHTML vs textContent for script text](http://jsperf.com/innerhtml-vs-textcontent-for-script-text)
		- [Long String Concatenation](http://jsperf.com/ya-string-concat)
		- Loading...

		[⬆ back to top](#table-of-contents)


		## Resources


		Read This

		- [Annotated ECMAScript 5.1](http://es5.github.com/)

		Other Styleguides

		- [Google JavaScript Style Guide](http://google-styleguide.googlecode.com/svn/trunk/javascriptguide.xml)
		- [jQuery Core Style Guidelines](http://docs.jquery.com/JQuery_Core_Style_Guidelines)
		- [Principles of Writing Consistent, Idiomatic JavaScript](https://github.com/rwldrn/idiomatic.js/)

		Other Styles

		- [Naming this in nested functions](https://gist.github.com/4135065) - Christian Johansen
		- [Conditional Callbacks](https://github.com/airbnb/javascript/issues/52)
		- [Popular JavaScript Coding Conventions on Github](http://sideeffect.kr/popularconvention/#javascript)

		Further Reading

		- [Understanding JavaScript Closures](http://javascriptweblog.wordpress.com/2010/10/25/understanding-javascript-closures/) - Angus Croll
		- [Basic JavaScript for the impatient programmer](http://www.2ality.com/2013/06/basic-javascript.html) - Dr. Axel Rauschmayer
		- [You Might Not Need jQuery](http://youmightnotneedjquery.com/) - Zack Bloom & Adam Schwartz
		- [ES6 Features](https://github.com/lukehoban/es6features) - Luke Hoban

		Books

		- [JavaScript: The Good Parts](http://www.amazon.com/JavaScript-Good-Parts-Douglas-Crockford/dp/0596517742) - Douglas Crockford
		- [JavaScript Patterns](http://www.amazon.com/JavaScript-Patterns-Stoyan-Stefanov/dp/0596806752) - Stoyan Stefanov
		- [Pro JavaScript Design Patterns](http://www.amazon.com/JavaScript-Design-Patterns-Recipes-Problem-Solution/dp/159059908X) - Ross Harmes and Dustin Diaz
		- [High Performance Web Sites: Essential Knowledge for Front-End Engineers](http://www.amazon.com/High-Performance-Web-Sites-Essential/dp/0596529309) - Steve Souders
		- [Maintainable JavaScript](http://www.amazon.com/Maintainable-JavaScript-Nicholas-C-Zakas/dp/1449327680) - Nicholas C. Zakas
		- [JavaScript Web Applications](http://www.amazon.com/JavaScript-Web-Applications-Alex-MacCaw/dp/144930351X) - Alex MacCaw
		- [Pro JavaScript Techniques](http://www.amazon.com/Pro-JavaScript-Techniques-John-Resig/dp/1590597273) - John Resig
		- [Smashing Node.js: JavaScript Everywhere](http://www.amazon.com/Smashing-Node-js-JavaScript-Everywhere-Magazine/dp/1119962595) - Guillermo Rauch
		- [Secrets of the JavaScript Ninja](http://www.amazon.com/Secrets-JavaScript-Ninja-John-Resig/dp/193398869X) - John Resig and Bear Bibeault
		- [Human JavaScript](http://humanjavascript.com/) - Henrik Joreteg
		- [Superhero.js](http://superherojs.com/) - Kim Joar Bekkelund, Mads Mobæk, & Olav Bjorkoy
		- [JSBooks](http://jsbooks.revolunet.com/)
		- [Third Party JavaScript](http://manning.com/vinegar/) - Ben Vinegar and Anton Kovalyov

		Blogs

		- [DailyJS](http://dailyjs.com/)
		- [JavaScript Weekly](http://javascriptweekly.com/)
		- [JavaScript, JavaScript...](http://javascriptweblog.wordpress.com/)
		- [Bocoup Weblog](http://weblog.bocoup.com/)
		- [Adequately Good](http://www.adequatelygood.com/)
		- [NCZOnline](http://www.nczonline.net/)
		- [Perfection Kills](http://perfectionkills.com/)
		- [Ben Alman](http://benalman.com/)
		- [Dmitry Baranovskiy](http://dmitry.baranovskiy.com/)
		- [Dustin Diaz](http://dustindiaz.com/)
		- [nettuts](http://net.tutsplus.com/?s=javascript)

		[⬆ back to top](#table-of-contents)

		## In the Wild

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

		- Aan Zee: [AanZee/javascript](https://github.com/AanZee/javascript)
		- Airbnb: [airbnb/javascript](https://github.com/airbnb/javascript)
		- American Insitutes for Research: [AIRAST/javascript](https://github.com/AIRAST/javascript)
		- Compass Learning: [compasslearning/javascript-style-guide](https://github.com/compasslearning/javascript-style-guide)
		- DailyMotion: [dailymotion/javascript](https://github.com/dailymotion/javascript)
		- Digitpaint [digitpaint/javascript](https://github.com/digitpaint/javascript)
		- ExactTarget: [ExactTarget/javascript](https://github.com/ExactTarget/javascript)
		- Gawker Media: [gawkermedia/javascript](https://github.com/gawkermedia/javascript)
		- GeneralElectric: [GeneralElectric/javascript](https://github.com/GeneralElectric/javascript)
		- GoodData: [gooddata/gdc-js-style](https://github.com/gooddata/gdc-js-style)
		- Grooveshark: [grooveshark/javascript](https://github.com/grooveshark/javascript)
		- How About We: [howaboutwe/javascript](https://github.com/howaboutwe/javascript)
		- Mighty Spring: [mightyspring/javascript](https://github.com/mightyspring/javascript)
		- MinnPost: [MinnPost/javascript](https://github.com/MinnPost/javascript)
		- ModCloth: [modcloth/javascript](https://github.com/modcloth/javascript)
		- Money Advice Service: [moneyadviceservice/javascript](https://github.com/moneyadviceservice/javascript)
		- Muber: [muber/javascript](https://github.com/muber/javascript)
		- National Geographic: [natgeo/javascript](https://github.com/natgeo/javascript)
		- National Park Service: [nationalparkservice/javascript](https://github.com/nationalparkservice/javascript)
		- Orion Health: [orionhealth/javascript](https://github.com/orionhealth/javascript)
		- Peerby: [Peerby/javascript](https://github.com/Peerby/javascript)
		- Razorfish: [razorfish/javascript-style-guide](https://github.com/razorfish/javascript-style-guide)
		- reddit: [reddit/styleguide/javascript](https://github.com/reddit/styleguide/tree/master/javascript)
		- REI: [reidev/js-style-guide](https://github.com/reidev/js-style-guide)
		- Ripple: [ripple/javascript-style-guide](https://github.com/ripple/javascript-style-guide)
		- SeekingAlpha: [seekingalpha/javascript-style-guide](https://github.com/seekingalpha/javascript-style-guide)
		- Shutterfly: [shutterfly/javascript](https://github.com/shutterfly/javascript)
		- TheLadders: [TheLadders/javascript](https://github.com/TheLadders/javascript)
		- Userify: [userify/javascript](https://github.com/userify/javascript)
		- Zillow: [zillow/javascript](https://github.com/zillow/javascript)
		- ZocDoc: [ZocDoc/javascript](https://github.com/ZocDoc/javascript)

		## Translation

		This style guide is also available in other languages:

		- :de: German: [timofurrer/javascript-style-guide](https://github.com/timofurrer/javascript-style-guide)
		- :jp: Japanese: [mitsuruog/javacript-style-guide](https://github.com/mitsuruog/javacript-style-guide)
		- :br: Portuguese: [armoucar/javascript-style-guide](https://github.com/armoucar/javascript-style-guide)
		- :cn: Chinese: [adamlu/javascript-style-guide](https://github.com/adamlu/javascript-style-guide)
		- :es: Spanish: [paolocarrasco/javascript-style-guide](https://github.com/paolocarrasco/javascript-style-guide)
		- :kr: Korean: [tipjs/javascript-style-guide](https://github.com/tipjs/javascript-style-guide)
		- :fr: French: [nmussy/javascript-style-guide](https://github.com/nmussy/javascript-style-guide)
		- :ru: Russian: [uprock/javascript](https://github.com/uprock/javascript)
		- :bg: Bulgarian: [borislavvv/javascript](https://github.com/borislavvv/javascript)

		## The JavaScript Style Guide Guide

		- [Reference](https://github.com/airbnb/javascript/wiki/The-JavaScript-Style-Guide-Guide)

		## Contributors

		- [View Contributors](https://github.com/airbnb/javascript/graphs/contributors)


		## License

		(The MIT License)

		Copyright (c) 2014 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.

		[⬆ back to top](#table-of-contents)

		# };
		- Deprecate JSBeautifier - JSCS has [an open issue](https://github.com/jscs-dev/node-jscs/issues/516) to add autoformatting, which will eliminate the need for JSBeautifier.

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