JavaScript Style Guide
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README.md

Jam3 JavaScript Style Guide

Make It Happen and Don't Fuck It Up

Table of Contents

  1. Types
  2. Objects
  3. Arrays
  4. Strings
  5. Functions
  6. Properties
  7. Variables
  8. Hoisting
  9. Conditional Expressions & Equality
  10. Blocks
  11. Comments
  12. Whitespace
  13. Commas
  14. Semicolons
  15. Type Casting & Coercion
  16. Naming Conventions
  17. Accessors
  18. Constructors
  19. Events
  20. Modules
  21. jQuery
  22. Testing
  23. Performance
  24. Resources
  25. In the Wild
  26. Translation
  27. The JavaScript Style Guide Guide
  28. Chat With Us About Javascript
  29. Contributors
  30. License

Types

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

    • string
    • number
    • boolean
    • null
    • undefined
    var foo = 1;
    var 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];
    var bar = foo;
    
    bar[0] = 9;
    
    console.log(foo[0], bar[0]); // => 9, 9

⬆ back to top

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'
    };

⬆ back to top

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;
    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.

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

⬆ back to top

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

    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

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

⬆ back to top

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');

⬆ back to top

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 per variable. It's easier to add new variable declarations this way, and you never have to worry about swapping out a ; for a , or introducing punctuation-only diffs.

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

    // bad
    var i, len, dragonball,
        items = getItems(),
        goSportsTeam = true;
    
    // bad
    var i;
    var items = getItems();
    var dragonball;
    var goSportsTeam = true;
    var len;
    
    // good
    var items = getItems();
    var goSportsTeam = true;
    var dragonball;
    var length;
    var i;
  • 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;
    }
  • Do not visually line up variables

    // bad
    var name           = 'Name';
    var longerName     = 'Longer Name';
    var evenLongerName = 'Even Longer Name';
    
    // good
    var name = 'Name';
    var longerName = 'Longer Name';
    var evenLongerName = 'Even Longer Name';

⬆ back to top

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.

⬆ back to top

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
    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.

⬆ back to top

Blocks

  • Use braces with all multi-line blocks.

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

⬆ back to top

Comments

  • Use /** ... */ to document public function definitions. 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;
    }
  • Use // for multiline comments when a single line comment is longer than 80 charachters. Or use /* .. */

    // bad
    // this method will return a fantabulous variable that you can use to do lots of calculations with. If you don't know how to use it see the docs at http://someFakeSite.com
    var fantabulousValue = fantabulous();
    
    // good
    // this method will return a fantabulous variable that you can use to do
    // lots of calculations with. If you don't know how to use it see the docs // at http://someFakeSite.com
    var fantabulousValue = fantabulous();
    
    // good
    /*
     * this method will return a fantabulous variable that you can use to do
     * lots of calculations with. If you don't know how to use it see the docs 
     * at http://someFakeSite.com
     */
    var fantabulousValue = fantabulous();
  • 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;
    }

**[⬆ 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. Use a leading dot, which
  emphasizes that the line is a method call, not a new statement.

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

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

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

  // bad
  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);
  ```

- Leave a blank line after blocks and before the next statement

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

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

  return baz;

  // bad
  var obj = {
    foo: function() {
    },
    bar: function() {
    }
  };
  return obj;

  // good
  var obj = {
    foo: function() {
    },

    bar: function() {
    }
  };

  return obj;
  ```

- Magic Numbers and Fancy Stuff should be commented. Magic Numbers are constant values used for calculations. Fancy Stuff are things out of the norm done with good reason.

  ```javascript
  // Magic Numbers
  
  // +10 to move over from border
  element.style.left = left + 10 + 'px';


  // Fancy Stuff

  // parseInt was the reason my code was slow.
  // Bitshifting the String to coerce it to a
  // Number made it a lot faster.
  var val = '10' >> 0;
  ```

**[⬆ back to top](#table-of-contents)**

## Commas

- Leading commas: **Nope.**

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

  // good
  var story = [
    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'
  ];
  ```

**[⬆ 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);

  // bad
  var hasAge = !!age;

  // good
  var hasAge = Boolean(age);

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

**[⬆ back to top](#table-of-contents)**


## Naming Conventions

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

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

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

  // bad
  var perc = 0;

  // good
  var percentage = 0;
  ```

- 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';
  ```

- Use a leading underscore `_` when naming private methods. Private methods should exist outside of the scope of object and should be invoked using the call method.

```javascript
var dog = {
  _name: 'Spot',

  bark: function(sound) {
    _bark.call( this, sound );
  }
};

function _bark(sound) {
  console.log(this._name + ':' + sound);
}
  • Boolean variables should prefixed with is or has.

    // bad
    var cat = false;
    var eggs = true;
    
    // good
    var isCat = false;
    var hasEggs = true;
  • When saving a reference to this use _this.

    // bad
    function() {
      var self = this;
      return function() {
        console.log(self);
      };
    }
    
    // bad
    function() {
      var that = this;
      return function() {
        console.log(that);
      };
    }
    
    // good
    function() {
      var _this = this;
      return function() {
        console.log(_this);
      };
    }
  • Name your functions. This is helpful for stack traces.

    // 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/ for more info.

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Accessors

  • Accessor functions for properties are not required.

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

    // bad
    dragon.age();
    
    // good
    dragon.getAge();
    
    // bad
    dragon.age(25);
    
    // good
    dragon.setAge(25);
  • If the property is a boolean, use isVal() or hasVal().

    // bad
    if (!dragon.age()) {
      return false;
    }
    
    dragon.age(true);
    
    // good
    if (!dragon.hasAge()) {
      return false;
    }
    
    drag.setHasAge(true);
  • It's okay to create get() and set() functions, but be consistent.

    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];
    };
  • Getters and Setters via properties can be used in non processor intensive operations. Should be defined via Object.defineProperty on a prototype

Object.defineProperty(ObjecCar.prototype, 'speed', {
  get: function() {
    return this._speed;
  },

  set: function(speed) {
    this._speed = speed;
  }
});

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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!

    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.

    // 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.

    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();
    };

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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
    });

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Modules

  • Modules should be built using the CommonJS pattern

    // Creating a module in ./doSomething.js
    module.exports = function doSomething() {
    
      console.log('BOO YA!');
    };
    // Consuming module from ./doSomething.js in another file
    var doSomething = require('./doSomething');
    
    doSomething();
  • Resuable modules should be distributed on NPM

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jQuery

  • You should shy away from using jQuery. Instead use modules off NPM like:
    • dom-select
    • dom-style
    • dom-tree
    • dom-event
  • Visit https://github.com/npm-dom for more info.

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Performance

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Resources

Read This

Tools

Other Styleguides

Other Styles

Further Reading

Books

Blogs

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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.

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};