JavaScript Style Guide

A mostly reasonable approach to JavaScript

Best Practices
- Semicolons;
- Style Checking
- Linting
- Events
- Modules
- jQuery
- ECMAScript 5 Compatibility
- Testing
- [console statements](#console statements)
- Comments
- Variable Naming
- Polyfills
- Everyday Tricks
- Performance
Syntax
Resources
License

Best Practices

Semicolons`;`

Automatic Semicolon Insertion (ASI) is a complicated feature. But, writing a ; at the end of every line is painful. And the rules aren't that complex to learn. Don't bother with the semi-colons.

Style Checking

Tools like jscs can strictly enforce a code style. This makes it easy to ensure that developers can look at code they didn't write and more quickly understand what's going on. However, style-checking failures can be painful to deal with. Leave the implementation up to the team working the the project.

Generally, these work well in small projects. A sample .jscrc is in this repo.

Linting

Linting is always a great idea. Don't use a linter that's super opinionated about how the code should be styled, like jslint. Instead, use something more lenient like jshint or eslint.

A few tips when using JSHint

Declare a .jshintignore file and include node_modules, bower_components, and the like
You should use a .jshintrc file to keep your rules together. See the one in this repo.

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:

// 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
})

Modules

write all modules in the CommonJs style. We'll use browserify to turn it into a UMD module where necessary.
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.

// fancyInput/fancyInput.js
'use strict'

var previousFancyInput = global.FancyInput

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

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

module.exports = FancyInput

jQuery

Prefix jQuery object variables with a $.

// bad
var sidebar = $('.sidebar')

// good
var $sidebar = $('.sidebar')

Cache jQuery lookups.

// 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

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')

ECMAScript 5 Compatibility [es5]

Refer to Kangax's ES5 compatibility table
Note that you're probably using a library that includes es5shim, this means that you can probably freely use es5 methods.

Testing

Yup.
```
function(){
  return true
}
```

`console` statements [console statements]

Preferably bake console statements into a service that can easily be disabled in production. Alternatively, don't ship any console.log printing statements to production distributions.

Comments

Comments aren't meant to explain what the code does. Good code is supposed to be self-explanatory. If you're thinking of writing a comment to explain what a piece of code does, chances are you need to change the code itself. The exception to that rule is explaining what a regular expression does. Good comments are supposed to explain why code does something that may not seem to have a clear-cut purpose.

Bad

// create the centered container
var p = $('<p/>')
p.center(div)
p.text('foo')

Good

var $container = $('<p/>')
  , contents = 'foo'

$container.center(parent)
$container.text(contents)

megaphone.on('data', function(value){
  // the megaphone periodically emits updates for container
  container.text(value)
})

var numeric = /\d+/ // one or more digits somewhere in the string
if (numeric.test(text)){
  console.log('so many numbers!')
}

Commenting out entire blocks of code should be avoided entirely, that's why you have version control systems in place!

Variable Naming

Variables must have meaningful names so that you don't have to resort to commenting what a piece of functionality does. Instead, try to be expressive while succinct, and use meaningful variable names.

Bad

function a (x, y, z) {
  return z * y / x
}
a(4, 2, 6);
// <- 3

Good

function ruleOfThree (had, got, have) {
  return have * got / had
}
ruleOfThree(4, 2, 6)
// <- 3

Polyfills

Where possible use the native browser implementation and include a polyfill that provides that behavior for unsupported browsers. This makes the code easier to work with and less involved in hackery to make things just work.

If you can't patch a piece of functionality with a polyfill, then wrap all uses of the patching code in a globally available method that is accessible from everywhere in the application.

Everyday Tricks

Use || to define a default value. If the left-hand value is [falsy][29] then the right-hand value will be used.

function a(value){
  var defaultValue = 33
  var used = value || defaultValue
}

Use .bind to partially-apply functions.

var sum = function sum(a, b){
    return a + b
  }
  , addSeven = sum.bind(null, 7)

addSeven(6)
// <- 13

Use Array.prototype.slice.call to cast array-like objects to true arrays.

var args = [].slice.call(arguments)

Use event emitters on all the things!

var emitter = new Backbone.Events()

$body.on('click', function onBodyClick(e){
  emitter.trigger('click', e.target)
})

emitter.on('click', function onEmitterClick(elem) {
  console.log(elem)
})

// simulate click
emitter.trigger('click', document.body)

Use Function() as a "no-op".

function onThingHappended(cb){
  setTimeout(cb || Function(), 2000)
}

Performance

Syntax

Types

Primitives: When you access a primitive type you work directly on its value
- string
- number
- boolean
- null
- undefined
```
var foo = 1
  , bar = foo

bar = 9

console.log(foo, bar) // => 1, 9
```

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

object
array
function

var foo = [1, 2]
  , bar = foo

bar[0] = 9

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

Objects

Use the literal syntax for object creation.

// bad
var item = new Object()

// good
var item = {}

Don't use reserved words as keys. It won't work in IE8. More info

// bad
var superman = {
  default: {clark: 'kent'}
  , private: true
}

// good
var superman = {
  defaults: {clark: 'kent'}
  , hidden: true
}

Use readable synonyms in place of reserved words.

// bad
var superman = {
  class: 'alien'
}

// bad
var superman = {
  klass: 'alien'
}

// good
var superman = {
  type: 'alien'
}

Arrays

Use the literal syntax for array creation

// bad
var items = new Array()

// good
var items = []

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

var someStack = []

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

// good
someStack.push('abracadabra')

When you need to copy an array use Array#slice. jsPerf

var len = items.length
  , itemsCopy = []
  , 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.

function trigger(){
  var args = Array.prototype.slice.call(arguments)
  …
}

Strings

Use single quotes '' for strings

// bad
var name = "Bob Parr"

// good
var name = 'Bob Parr'

// bad
var fullName = "Bob " + this.lastName

// good
var fullName = 'Bob ' + this.lastName

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 & Discussion

// 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 programatically building up a string, use Array#join instead of string concatenation. Mostly for IE: jsPerf.

var items
  , messages
  , length
  , 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>'
}

Functions

Function expressions:

// 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.

// 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.

// bad
function nope(name, options, arguments){
  // …stuff…
}

// good
var yup = function yup(name, options, args){
  // …stuff…
}

Always prefer named functions This makes debugging much easier.
You should assign a function to a variable. This makes hoisting easier to reason about.

Never put spaces immediately after an opening parens or immediately before a closing parens.

// bad
var bad = function ( badness, devils, misery ) {

}

// good
var good = function good(happiness, heaven, cheesecake){

}

Avoid creating functions that accept more than 3 arguments. You should probably pass a single options argument instead.

// bad
var manyThings = function manyThings(first, second, moar, evenMoar){

}

// good
var manyThings = function manyThings(options){
  /*
  options.first
  options.second
  etc…
  */
}

Properties

Use dot notation when accessing properties.

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.

var luke = {
  jedi: true
  , age: 28
}

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

var isJedi = getProp('jedi')

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.
```
// bad
superPower = new SuperPower()

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

Use one var declaration for multiple variables and declare each variable on a newline.

// bad
var items = getItems()
var goSportsTeam = true
var dragonball = 'z'

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

Declare unassigned variables last. This is helpful when later on you might need to assign a variable depending on one of the previous assigned variables. You should give "unassigned" variables a default value. This allows modern JS engines like V8 to better optimize. It also makes the code more readable.

// bad
var i, len, dragonball
  , items = getItems()
  , goSportsTeam = true

// bad
var i, items = getItems()
  , dragonball
  , goSportsTeam = true
  , len

// good
var items = getItems()
  , goSportsTeam = true
  , dragonball = {}
  , length = 0
  , i = 0

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

// 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
}

Hoisting

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

// 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.

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.

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.

function example(){
  superPower() // => Flying

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

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

Conditional Expressions & Equality [conditional-expressions]

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

Use shortcuts.

// 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 by Angus Croll

Blocks

Single line blocks don't require braces, but should be easy to read. If your single line extends more than 80 characters, break into two lines, and indent the contents of the block.

// bad
if (test){
  return false
}

// bad
if (test)
  return false

// good
if (test) return false


// bad
if (test && test.arg === doSomethingWith(5) && puppies() === 'cute') ciderHouse = true

// good
if (test && test.arg === doSomethingWith(5) && puppies() === 'cute')
  ciderHouse = true

// bad
function(){ return false }

// good
function(){
  return false
}

Comments

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

// 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.

// 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

function Calculator(){

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

  return this
}

Use // TODO: to annotate solutions to problems

function Calculator(){

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

  return this
}




### Whitespace

- Use soft tabs set to 2 spaces

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

  // bad
  function(){
  ∙var name
  }

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

- Place no spaces 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
  ```

- Place an empty newline at the end of the file.

  ```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)
  ```


### Commas

- Leading commas: **Hell yes.**
- [Read why comma first is better](https://gist.github.com/isaacs/357981/)

  ```javascript
  // bad
  var once,
      upon,
      aTime

  // good
  var once
    , upon
    , aTime

  // 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'
  ]
  ```



### Semicolons

- **NO.**
- ASI means that you almost never need semicolons. Leave 'em out and live free! JsHint will catch nearly any error you might make.

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

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

  // good
  var a

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

### 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)

  // better
  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.
- **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)

  ```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
  ```

- Booleans:

  ```javascript
  var age = 0

  // bad
  var hasAge = new Boolean(age)

  // good
  var hasAge = Boolean(age)

  // better
  var hasAge = !!age
  ```



### 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'
  })
  ```

- Use a leading underscore `_` when naming private properties

  ```javascript
  // bad
  this.__firstName__ = 'Panda'
  this.firstName_ = 'Panda'

  // good
  this._firstName = 'Panda'
  ```

- When saving a reference to `this` use `self`. Avoid using self unless absolutely necessary. Pefer `_.bind()`

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

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

  // bad
  function(){
    var self = this
    self.thing = true
  }

  // good
  function(){
    var self = this
    this.thing = true
    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)
  }
  ```



### Accessors

- Accessor functions for properties are not required
- If you do make accessor functions use getVal() and setVal('hello')

  ```javascript
  // bad
  dragon.age()

  // good
  dragon.getAge()

  // bad
  dragon.age(25)

  // good
  dragon.setAge(25)
  ```

- 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]
  }
  ```



### 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()
  }
  ```



## Resources


### Read This [read-this]

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

### Other Styleguides [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/)
- This style guide is based on [AirBnB's style guide](https://github.com/airbnb/javascript)

### Other Styles [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 [further-readingj]

- [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

### 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/)

### 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)


## License

Based on the style guides from [Airbnb](https://github.com/airbnb/javascript) and [bevacqua/js](https://github.com/bevacqua/js)

(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.

**[[⬆]](#TOC)**

cstumph/styleguide-js

JavaScript Style Guide

Table of Contents

Best Practices

Semicolons`;`

Style Checking

Linting

A few tips when using JSHint

Events

Modules

jQuery

ECMAScript 5 Compatibility [es5]

Testing

`console` statements [console statements]

Comments

Bad

Good

Variable Naming

Bad

Good

Polyfills

Everyday Tricks

Performance

Syntax

Types

Objects

Arrays

Strings

Functions

Properties

Variables

Hoisting

Conditional Expressions & Equality [conditional-expressions]

Blocks

Comments

cstumph/styleguide-js

JavaScript Style Guide

Table of Contents

Best Practices

Semicolons;

Style Checking

Linting

A few tips when using JSHint

Events

Modules

jQuery

ECMAScript 5 Compatibility [es5]

Testing

console statements [console statements]

Comments

Bad

Good

Variable Naming

Bad

Good

Polyfills

Everyday Tricks

Performance

Syntax

Types

Objects

Arrays

Strings

Functions

Properties

Variables

Hoisting

Conditional Expressions & Equality [conditional-expressions]

Blocks

Comments

Semicolons`;`

`console` statements [console statements]