eslint-config-saturized

JavaScript Style Guide

Types
Objects
Arrays
Strings
Functions
Properties
Variables
Hoisting
Conditional Expressions & Equality
Blocks
Comments
Whitespace
Commas
Semicolons
Type Casting & Coercion
Naming Conventions
Accessors
Constructors
Events
Modules
jQuery

Types

Primitives: When you access a primitive type you work directly on its value
- string
- number
- boolean
- null
- undefined

#!javascript
    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

#!javascript
    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.

#!javascript
    // bad
    var item = new Object();

    // good
    var item = {};

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

#!javascript
    // bad
    var superman = {
      default: { clark: 'kent' },
      private: true
    };

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

Use readable synonyms in place of reserved words.

#!javascript
    // 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

#!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

#!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

Strings

Use single quotes '' for strings

#!javascript
    // 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

#!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.

#!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

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.

#!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

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

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. 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.

#!javascript
    // 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.

#!javascript
    // 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.

#!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;
    }

⬆ back to top

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 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

#!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 by Angus Croll

⬆ back to top

Blocks

Always use curly braces for blocks, avoid one-line statements

#!javascript
    // bad
    if (test)
      return false;

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

    // bad
    function() { return false; }

    // good
    function() {
      return false;
    }

⬆ back to top

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

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

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):

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

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

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, 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, but Bitshift operations always return a 32-bit integer (source). Bitshift can lead to unexpected behavior for integer values larger than 32 bits. Discussion. Largest signed 32-bit Int is 2,147,483,647:

#!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

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.

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

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

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

For jQuery use '$this'

#!javascript
    // bad
    $('li').each(function() {
      self = $(this);
      console.log(self);
    });

    // good
    function() {
      $('li').each(function() {
        $this = $(this);
        console.log($this);
      });
    }

It's desirable to name your functions. This is helpful for stack traces.

#!javascript
    // not recommended
    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.

⬆ back to top

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];
    };

⬆ back to top

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

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:

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

    ...

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

prefer:

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

    ...

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

⬆ back to top

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
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

jQuery

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
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

eslint-config-saturized

JavaScript Style Guide

Types

Objects

Arrays

Strings

Functions

Properties

Variables

Hoisting

Conditional Expressions & Equality

Blocks

Comments

Whitespace

Commas

Semicolons

Type Casting & Coercion

Naming Conventions

Accessors

Constructors

Events

Modules

jQuery

Readme

Keywords

Package Sidebar

Install

Repository

Homepage

Weekly Downloads

Version

License

Last publish

Collaborators

eslint-config-saturized

JavaScript Style Guide

Types

Objects

Arrays

Strings

Functions

Properties

Variables

Hoisting

Conditional Expressions & Equality

Blocks

Comments

Whitespace

Commas

Semicolons

Type Casting & Coercion

Naming Conventions

Accessors

Constructors

Events

Modules

jQuery

Readme

Keywords

Package Sidebar

Install

Repository

Homepage

DownloadsWeekly Downloads

Version

License

Last publish

Collaborators

Weekly Downloads