uShip JavaScript Style Guide () {

A mostly reasonable approach to JavaScript, based on AirBnb's 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
ES5 Compatibility
Testing
Performance
Resources
In the Wild
Translation
The JavaScript Style Guide Guide
Contributors
License

Types

Primitives: When you access a primitive type you work directly on its value
- string
- number
- boolean
- null
- undefined
```
let 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
```
let foo = [1, 2],
    bar = foo;

bar[0] = 9;

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

Use the literal syntax for object creation.

// bad
let item = new Object();

// good
let item = {};

(ES6) Use enhanced object literal instantiation to reduce boilerplate when assigning values to properties, methods, and dynamically computed property names:

// bad
let private = true,
    weakness = 'kryptonite';

let superman = {
    private: private,
    fly: function () {
        console.log('Faster than a speeding bullet');
    }
}

superman[weakness] = true;

// good
let private = true,
    weakness = 'kryptonite';

let superman = {
    private,
    fly () {
        console.log('Faster than a speeding bullet');
    },
    [weakness]: true
}

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

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

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

Use readable synonyms in place of reserved words.

// bad
let superman = {
    class: 'alien'
};

// bad
let superman = {
    klass: 'alien'
};

// good
let superman = {
    type: 'alien'
};

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Arrays

Use the literal syntax for array creation

// bad
let items = new Array();

// good
let items = [];

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

let someStack = [];


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

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

(ES6) To copy an array, use the spread operator:

let items = [1, 2, 3],
    itemsCopy;

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

// good
itemsCopy = [...items];

(ES5) In ES5 environments, use Array#slice to copy an array.

var items = [1, 2, 3],
    itemsCopy;

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

// good
itemsCopy = items.slice();

(ES6) To convert an array-like object to an array, use the spread operator.

let nodeList = document.getElementsByTagName('a'),
    nodesArray = [...nodesList];

(ES5) To convert an array-like object to an array in ES5 environments, use Array#slice.

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

(ES5) To convert an array-like object to an array in ES5 environments, use Array#slice.

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

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Strings

Use single quotes '' for strings

// bad
const NAME = "Bob Parr";

// good
const NAME = 'Bob Parr';

(ES6) Use template strings for interpolating variables in strings

// bad
let fullName = 'Bob ' + this.lastName;

// good
let fullname = `Bob ${this.lastName}`;

(ES6) Strings longer than 80 characters should be written across multiple lines using template strings:

// bad
let 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
let 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
let 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.`;

(ES5) Strings longer than 80 characters should be written across multiple lines using string concatenation in ES5 environments.

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.

let items,
    messages,
    length;

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

    return items + '</ul>';
}

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

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

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

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Functions

There are lots of ways to declare and use functions. Here's a list:

// anonymous function expression
let anonymous = function () {
    return true;
};

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

// arrow function expression
let dogFilter = animal => typeof animal === 'Dog';

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

// function declaration
function greetings (yourName) {
    console.log(`Glad you could join us, ${yourName}`);
}

Um, that's a lot. Which to use? Here are some rules of thumb:
(ES6) For simple callbacks and functions passed as parameters, use arrow function shorthand. Arrow functions are lexically scoped, which makes them great for things like event handlers:
```
// bad
let self = this;
$('#hit-me').on('click', function () { self.hitCount++; });

// good
$('#hit-me').on('click', e => this.hitCount++);
```
For multiline functions, use function declarations. Function declarations are hoisted, so you can use the functions anywhere in the scope where they are declared.
```
// bad
let mapMyLocation = function () {
    //do a lot of stuff
}

// good
function mapMyLocation () {
    // do a lot of stuff
}
```

Don't abuse function parameters by deeply nesting anonymous functions. Instead, declare the function in the top-level scope and pass it by name.

// bad
let contents;
fs.readFile('first.txt', function (err, data) {
    if (err) {
        fs.readFile('url.txt', function (err, data) {
            if (!err) {
                http.get(data).then(function (resp) {
                    contents = resp.body;
                });
            }
        });
    } else {
        contents = data;
    }
});

// good
let contents;
fs.readFile('first.txt', handleFileRead);

function handleFileRead (err, data) {
    if (err) {
        fs.readFile('url.txt', handleFallbackRead);
    } else {
        contents = data;
    }
}

function handleFallbackRead (err, data) {
    if (err) return;
    http.get(data).then(resp => contents = resp.body);
}

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
let test;
if (currentUser) {
    test = function test () {
        console.log('Yup.');
    };
}

(ES6) Prefer the use of rest params instead of the arguments keyword.

// bad
function stuff () {
    console.log(arguments.length);
}

// good
function betterStuff (...args) {
    console.log(args.length);
}

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...
}

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Properties

Use dot notation when accessing properties.

let luke = {
    jedi: true,
    age: 28
};

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

// good
let isJedi = luke.jedi;

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

let luke = {
    jedi: true,
    age: 28
};

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

let isJedi = getProp('jedi');

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Variables

Always use var, let or const to declare variables. Not doing so will result in strict mode errors.
```
// bad
superPower = new SuperPower();

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

(ES6) Use only let or const instead of var. If you have a specific need for a function-scoped variable instead of a block-scoped one, write a comment explaining why.

// bad
var howManyTimes = 5;
for (var i = 0; i < howManyTimes; i++) {
    ...
}

// good
const HOW_MANY_TIMES = 5;
for (let i = 0; i < howManyTimes, i++) {
    ...
}

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

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

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

(ES6) Use one const declaration per line, to emphasize the immutability of the assignment.

// bad
const SHAPE = 'circle',
    WEIGHT = 25;

// good
const SHAPE = 'circle';
const WEIGHT = 25;

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. One variable per line. Move multiline declarations -- like object literals -- to their own let or var expression.

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

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

// bad
let items = getItems(),
    startingInventory = {
        potions: 10,
        weapons: 5,
        staffs: 1
    },
    dragonball;

// good
let items = getItems(),
    goSportsTeam = true,
    dragonball,
    length,
    i;

// good
let items = getItems(),
    dragonball;

let startingInventory = {
    potions: 10,
    weapons: 5,
    staffs: 1
};

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..

    let name = getName();

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

    return name;
}

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

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

    //..other stuff..

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

    return name;
}

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

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

    return true;
}

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

    let name = getName();

    return true;
}

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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
    let 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 () {
    let 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

    let 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

    let 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

    let 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

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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

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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;
}

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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
const ACTIVE = true;  // is current tab

// good
// is current tab
const ACTIVE = true;

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

    return type;
}

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

    // set the default type to 'no type'
    let 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;
}

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Whitespace

In general, keep lines short. Use newlines between blocks or chunks of related code.

// bad
this.weightUnits = ko.computed(() =>
    (this.systemOfMeasurement() === 'Metric') ? uship.localization['MainKg'] : uship.localization['MainLbs']
);
function anotherFunction () {
    let foo = 1;
}

// good
this.weightUnits = ko.computed(() =>
    (this.systemOfMeasurement() === 'Metric') ?
        uship.localization['MainKg'] :
        uship.localization['MainLbs']
);

function anotherFunction () {
    let foo = 1;
}

Use soft tabs set to 4 spaces. Don't mix hard tabs and spaces.

// bad
function() {
____var name;
}

// bad
function() {
∙∙var name;
}

// bad
function() {
∙var name;
}

// good
function() {
∙∙∙∙var name;
}

Place 1 space before the leading brace. For function declarations, place 1 space between the function keyword and the arguments list.

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

// 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.

// bad
let x=y+5;

// good
let x = y + 5;

Use a newline between key/value pairs in an object literal. Place 1 space between keys and values. You can choose to tab-align values as long as the result is more readable.

// bad
var dog = { breed: 'Maltese', color: 'white', age: '3 years' };

// bad
let dog = { 
    breed:'Maltese',
    color:'white',
    age:'3 years' 
};

// good
let dog = { 
    breed: 'Maltese',
    color: 'white',
    age: '3 years' 
};

// bad
let dog = { 
    breed:                                             'Maltese',
    color:                                             'white',
    age:                                               '3 years',
    aReallyLongPropertyNameMakesAlignmentHardToRead: true
};

// acceptable
let dog = { 
    breed:    'Maltese',
    color:    'white',
    age:      '3 years',
    adorable: 'obviously'
};

Use indentation when making long method chains.

// 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);

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Commas

Leading commas: Nope.

// bad
let once
  , upon
  , aTime;

// good
let once,
    upon,
    aTime;

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

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

// bad
let heroes = [
    'Batman',
    'Superman',
];

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

// good
let heroes = [
    'Batman',
    'Superman'
];
```

**[&#8593; Back to top](#TOC)**

Semicolons

Yup. Javascript will automatically insert semicolons -- that it's they're optional in the strict sense. But leaving out semicolons can cause some pernicious bugs, particularly when multiple people are working on the same code, or when not everyone is an expert on the edge case rules for semicolon insertion. So for consistency's sake, always use them.
```
// bad
(function () {
    let name = 'Skywalker'
    return name
})()

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

// good
;(function () {
    let name = 'Skywalker';
    return name;
})();
```
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Type Casting & Coercion

Perform type coercion at the beginning of the statement.

Strings:

//  => this.reviewScore = 9;

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

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

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

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

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

let inputValue = '4';

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

// bad
let val = +inputValue;

// bad
let val = inputValue >> 0;

// bad
let val = parseInt(inputValue);

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

Booleans:

let age = 0;

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

// good
let hasAge = Boolean(age);

// good
let hasAge = !!age;

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Naming Conventions

Avoid single letter names. Be descriptive with your naming.

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

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

Use camelCase when naming objects, functions, and instances

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

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

Use PascalCase when naming constructors or classes

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

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

// good

class User {

    constructor (options) {
        this.name = options.name;
    }

}

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

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

Use a leading underscore _ when naming private properties

// bad
this.__firstName__ = 'Panda';
this.firstName_ = 'Panda';

// good
this._firstName = 'Panda';

When saving a reference to this use self. Prefer arrow function expressions or bind to replace the need for saving a reference to this. Stick to a single paradigm -- don't mix this and self in the same context.

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

function () {
    let self = this;
    this.trait = 'Inconsistency';
    return function () {
        console.log(self);
    };
}

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

// better
function () {
    return function () {
        console.log(this);
    }.bind(this);
}

// best
function () {
    return () => console.log(this);
}

Name your functions. This is helpful for stack traces. (You don't have to worry about this if you use function declarations as recommended.)
```
// bad
let log = function (msg) {
    console.log(msg);
};

// good
let log = function log (msg) {
    console.log(msg);
};
```
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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, make the property name a "statement of fact" using a prefix like "is", "has", or "should"

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

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

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

class Jedi {
    constructor (options) {
        options || (options = {});
        var lightsaber = options.lightsaber || 'blue';
        this.set('lightsaber', lightsaber);
    }

    set (key, val) {
        this[key] = val;
    }

    get (key) {
        return this[key];
    }
}

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Classes and Constructors

(ES6) Use the class syntax instead of constructor functions and prototypes

    // old
    function Jedi (options) {
        ForceUser.call(this);
        this.name = options.name;
    }

    Jedi.prototype = Object.create(ForceUser);

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

    // preferred
    class Jedi : ForceUser {
        constructor (options) {
            this.name = options.name;
        }

        jump () {
            this.jumping = true;
        }
    }

Methods can return this to help with method chaining.

// bad
class Jedi {
    jump () {
      this.jumping = true;
      return true;
    }

    setHeight (height) {
      this.height = height;
    }
}

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

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

    setHeight (height) {
      this.height = height;
      return this;
    }
}

let 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.

class Jedi {

    constructor (options) {
        options || (options = {});
        this.name = options.name || 'no name';
    }

    getName () {
        return this.name;
    }

    toString () {
        return 'Jedi - ' + this.getName();
    }
}

(ES5) 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');
};

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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', (e, listingId) => /* do something with listingId */);

prefer:

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

...

$(this).on('listingUpdated', (e, listingId) => /* do something with listingId */);

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Modules

Wrap the function expression in parentheses.
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 name should match the name of the single export. Casing should follow the same rules as the export -- e.g. a module that exports a constructor should be PascalCase.
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

;(function (global, $) {
    'use strict';

    let previousFancyInput = global.FancyInput;

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

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

    global.FancyInput = FancyInput;
})(window, window.jQuery);

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jQuery

Don't prefix jQuery object variables with a $.

// bad
let $sidebar = $('.sidebar');

// good
let sidebar = $('.sidebar');

Cache jQuery lookups.

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

    // ...stuff...

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

// good
function setSidebar () {
    let 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').hide();

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ECMAScript 5 Compatibility

Refer to Kangax's ES5 compatibility table

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Testing

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

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Resources

Read This

Annotated ECMAScript 5.1

Other Styleguides

Other Styles

Naming this in nested functions - Christian Johansen
Conditional Callbacks
Popular JavaScript Coding Conventions on Github

Further Reading

Understanding JavaScript Closures - Angus Croll
Basic JavaScript for the impatient programmer - Dr. Axel Rauschmayer

Books

JavaScript: The Good Parts - Douglas Crockford
JavaScript Patterns - Stoyan Stefanov
Pro JavaScript Design Patterns - Ross Harmes and Dustin Diaz
High Performance Web Sites: Essential Knowledge for Front-End Engineers - Steve Souders
Maintainable JavaScript - Nicholas C. Zakas
JavaScript Web Applications - Alex MacCaw
Pro JavaScript Techniques - John Resig
Smashing Node.js: JavaScript Everywhere - Guillermo Rauch
Secrets of the JavaScript Ninja - John Resig and Bear Bibeault
Human JavaScript - Henrik Joreteg
Superhero.js - Kim Joar Bekkelund, Mads Mobæk, & Olav Bjorkoy
JSBooks
Third Party JavaScript - Ben Vinegar and Anton Kovalyov

Blogs

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The JavaScript Style Guide Guide

Reference

Contributors

View Contributors

License

(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.

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