JavaScript Style Guide () {

A mostly reasonable approach to JavaScript

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 avoided and likely call for using a template system or similar.
If you have a good reason to have very long strings in code, they 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 messages = [{
    state: 'success',
    message: 'This one worked.'
},{
    state: 'success',
    message: 'This one worked as well.'
},{
    state: 'error',
    message: 'This one did not work.'
}];

var length = messages.length;

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

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

  return items + '</ul>';
}

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

  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
if (currentUser) {
  var 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
function yup (name, options, args) {
  // ...stuff...
}

[⬆]

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 a var declaration for each variable and declare each variable on a newline.

// 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 when not inconvenient. 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;
}

[⬆]

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 evalute 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

[⬆]

Control Flow

Put else/catch on same line as previous closing }.

// bad
if (test) {
  // stuff
}
else {
  // stuff
}

// good
if (test) {
  // stuff
} else {
  // stuff
}

// bad
try {
  // stuff
}
catch (e) {
  // stuff
}

// good
try {
  // stuff
} catch (e) {
  // stuff
}

Blocks

Use braces with all multi-line blocks.

// bad
if (test)
  return false;

// okay
if (test) return false;

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

// 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 emptyline 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;
}


  **[[⬆]](#TOC)**


## <a name='whitespace'>Whitespace</a>

- 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'
  });
  ```

- Place 1 space between the function name and parenthesis.

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

  // good
  function test () {
    console.log('test');
  }
  ```
- 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);
  ```

  **[[⬆]](#TOC)**

## <a name='commas'>Commas</a>

- 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'
  ];
  ```

  **[[⬆]](#TOC)**


## <a name='semicolons'>Semicolons</a>

- **Yup.**

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

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

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

  **[[⬆]](#TOC)**


## <a name='type-coercion'>Type Casting & Coercion</a>

- 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);
  ```

- Booleans:

  ```javascript
  var age = 0;

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

  // okay
  var hasAge = Boolean(age);

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

  **[[⬆]](#TOC)**


## <a name='naming-conventions'>Naming Conventions</a>

- 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 = {};
  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`.

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

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

- Name your functions for helpful stack traces.

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

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

  **[[⬆]](#TOC)**


## <a name='accessors'>Accessors</a>

- 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];
  };
  ```

  **[[⬆]](#TOC)**


## <a name='constructors'>Constructors</a>

- 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();
  };
  ```

  **[[⬆]](#TOC)**


## <a name='events'>Events</a>

- 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
  });
  ```

**[[⬆]](#TOC)**


## <a name='jquery'>jQuery</a>

- Prefix jQuery object variables with a `$`.

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

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

- 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
  $('.sidebar', 'ul').hide();

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

  // good
  $('.sidebar ul').hide();

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

  // good (slower)
  $sidebar.find('ul');

  // good (faster)
  $($sidebar[0]).find('ul');
  ```

  **[[⬆]](#TOC)**

## <a name='resources'>Resources</a>


**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)

**Further Reading**

- [Understanding JavaScript Closures](http://javascriptweblog.wordpress.com/2010/10/25/understanding-javascript-closures/) - Angus Croll

**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

**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)

**[[⬆]](#TOC)**

## <a name='guide-guide'>The JavaScript Style Guide Guide</a>

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

## <a name='authors'>Contributors</a>

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


## <a name='license'>License</a>

(The MIT License)

Copyright (c) 2012 Airbnb

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

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

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

**[[⬆]](#TOC)**

# };

Name		Name	Last commit message	Last commit date
Latest commit History 156 Commits
linters/SublimeLinter		linters/SublimeLinter
README.md		README.md

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

linters/SublimeLinter

linters/SublimeLinter

README.md

README.md

Repository files navigation

JavaScript Style Guide () {

Table of Contents

Objects

Arrays

Strings

Functions

Properties

Variables

Conditional Expressions & Equality

Control Flow

Blocks

Comments

About

Releases

Packages

spredfast/javascript

Folders and files

Latest commit

History

Repository files navigation

JavaScript Style Guide () {

About

Resources

Stars

Watchers

Forks