GitHub - MinnPost/javascript: JavaScript Style Guide (original) (raw)
MinnPost JavaScript Style Guide() {
Borrowed from AirBnB.
A mostly reasonable approach to JavaScript
Table of Contents
- Types
- Objects
- Arrays
- Strings
- Functions
- Properties
- Variables
- Hoisting
- Conditional Expressions & Equality
- Blocks
- Comments
- Whitespace
- Leading Commas
- Semicolons
- Type Casting & Coercion
- Naming Conventions
- Accessors
- Constructors
- 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
var foo = 1,
bar = foo;
bar = 9;
console.log(foo, bar); // => 1, 9
- Complex: When you access a complex type you work on a reference to its value
object
array
function
var foo = [1, 2],
bar = foo;
bar[0] = 9;
console.log(foo[0], bar[0]); // => 9, 9
[⬆]
Objects
- Use the literal syntax for object creation.
// bad
var item = new Object();
// good
var item = {}; - Don't use reserved words as keys.
// bad
var superman = {
class: 'superhero',
default: { clark: 'kent' },
private: true
};
// good
var superman = {
klass: 'superhero',
defaults: { clark: 'kent' },
hidden: true
};
[⬆]
Arrays
- Use the literal syntax for array creation
// bad
var items = new Array();
// good
var items = []; - If you don't know array length use Array#push.
var someStack = [];
// bad
someStack[someStack.length] = 'abracadabra';
// good
someStack.push('abracadabra'); - When you need to copy an array use Array#slice. jsPerf
var len = items.length,
itemsCopy = [],
i;
// bad
for (i = 0; i < len; i++) {
itemsCopy[i] = items[i];
}
// good
itemsCopy = items.slice(); - To convert an array-like object to an array, use Array#slice.
function trigger() {
var args = Array.prototype.slice.call(arguments);
...
}
[⬆]
Strings
- Use single quotes
''
for strings
// bad
var name = "Bob Parr";
// good
var name = 'Bob Parr';
// bad
var fullName = "Bob " + this.lastName;
// good
var fullName = 'Bob ' + this.lastName; - Strings longer than 80 characters should be written across multiple lines using string concatenation.
- Note: If overused, long strings with concatenation could impact performance. jsPerf & Discussion
// bad
var errorMessage = 'This is a super long error that was thrown because of Batman. When you stop to think about how Batman had anything to do with this, you would get nowhere fast.';
// bad
var errorMessage = 'This is a super long error that \
was thrown because of Batman. \
When you stop to think about \
how Batman had anything to do \
with this, you would get nowhere \
fast.';
// good
var errorMessage = 'This is a super long error that ' +
'was thrown because of Batman.' +
'When you stop to think about ' +
'how Batman had anything to do ' +
'with this, you would get nowhere ' +
'fast.'; - When programatically building up a string, use Array#join instead of string concatenation. Mostly for IE: jsPerf.
var items,
messages,
length, i;
messages = [{
state: 'success',
message: 'This one worked.'
},{
state: 'success',
message: 'This one worked as well.'
},{
state: 'error',
message: 'This one did not work.'
}];
length = messages.length;
// bad
function inbox(messages) {
items = '- ';
- ' + messages[i].message + ' ';
for (i = 0; i < length; i++) {
items += '
}
return items + '
}
// good
function inbox(messages) {
items = [];
for (i = 0; i < length; i++) {
items[i] = messages[i].message;
}
return '- ' + items.join('
- ') + '
}
[⬆]
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 thearguments
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 one
var
declaration for multiple variables and declare each variable on a newline.
// bad
var items = getItems();
var goSportsTeam = true;
var dragonball = 'z';
// good
var items = getItems(),
goSportsTeam = true,
dragonball = 'z'; - Declare unassigned variables last. This is helpful when later on you might need to assign a variable depending on one of the previous assigned variables.
// bad
var i, len, dragonball,
items = getItems(),
goSportsTeam = true;
// bad
var i, items = getItems(),
dragonball,
goSportsTeam = true,
len;
// good
var items = getItems(),
goSportsTeam = true,
dragonball,
length,
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;
}
[⬆]
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 oftrue
is not hoisted.
function example() {
console.log(declaredButNotAssigned); // => undefined
var declaredButNotAssigned = true;
}
// The interpreter is hoisting the variable
// declaration to the top of the scope.
// Which means our example could be rewritten as:
function example() {
var declaredButNotAssigned;
console.log(declaredButNotAssigned); // => undefined
declaredButNotAssigned = true;
} - Anonymous function expressions hoist their variable name, but not the function assignment.
function example() {
console.log(anonymous); // => undefined
anonymous(); // => TypeError anonymous is not a function
var anonymous = function() {
console.log('anonymous function expression');
};
} - Named function expressions hoist the variable name, not the function name or the function body.
function example() {
console.log(named); // => undefined
named(); // => TypeError named is not a function
superPower(); // => ReferenceError superPower is not defined
var named = function superPower() {
console.log('Flying');
};
// the same is true when the function name
// is the same as the variable name.
function example() {
console.log(named); // => undefined
named(); // => TypeError named is not a function
var named = function named() {
console.log('named');
};
}
} - Function declarations hoist their name and the function body.
function example() {
superPower(); // => Flying
function superPower() {
console.log('Flying');
}
} - For more information refer to JavaScript Scoping & Hoisting by Ben Cherry
[⬆]
Conditional Expressions & Equality
- 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
[⬆]
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;
}
[⬆]
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 tag
// @return element
function make(tag) {
// ...stuff...
return element;
}
// good
/** - make() returns a new element
- based on the passed in tag name
- @param tag
- @return 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
orTODO
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 areFIXME -- need to figure this out
orTODO -- 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.
// 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 an empty newline at the end of the file.
// bad (function(global) { // ...stuff... })(this);
// good (function(global) { // ...stuff... })(this);
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);
Leading Commas
Nope.
// bad var once , upon , aTime; // good var once, upon, aTime; // bad var hero = { firstName: 'Bob' , lastName: 'Parr' , heroName: 'Mr. Incredible' , superPower: 'strength' }; // good var hero = { firstName: 'Bob', lastName: 'Parr', heroName: 'Mr. Incredible', superPower: 'strength' };
Semicolons
Yup.
// bad (function() { var name = 'Skywalker' return name })() // good (function() { var name = 'Skywalker'; return name; })(); // good ;(function() { var name = 'Skywalker'; return name; })();
Type Casting & Coercion
Perform type coercion at the beginning of the statement.
Strings:
// => 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.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.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); // good /** * parseInt was the reason my code was slow. * Bitshifting the String to coerce it to a * Number made it a lot faster. */ var val = inputValue >> 0;
Booleans:
var age = 0; // bad var hasAge = new Boolean(age); // good var hasAge = Boolean(age); // good var hasAge = !!age;
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 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
// 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// bad this.__firstName__ = 'Panda'; this.firstName_ = 'Panda'; // good this._firstName = 'Panda';
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); };
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; } // good if (!dragon.hasAge()) { return false; }
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]; };
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(); };
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.The file should be named with camelCase, live in a folder with the same name, and match the name of the single export.
Add a method called noConflict() that sets the exported module to the previous version and returns this one.
Always declare
'use strict';
at the top of the module.// fancyInput/fancyInput.js !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);
jQuery
Prefix jQuery object variables with a
$
.// bad var sidebar = $('.sidebar'); // good var <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>s</mi><mi>i</mi><mi>d</mi><mi>e</mi><mi>b</mi><mi>a</mi><mi>r</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">sidebar = </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">s</span><span class="mord mathnormal">i</span><span class="mord mathnormal">d</span><span class="mord mathnormal">e</span><span class="mord mathnormal">ba</span><span class="mord mathnormal" style="margin-right:0.02778em;">r</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>('.sidebar');
Cache jQuery lookups.
// bad function setSidebar() { $('.sidebar').hide(); // ...stuff... $('.sidebar').css({ 'background-color': 'pink' }); } // good function setSidebar() { var <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>s</mi><mi>i</mi><mi>d</mi><mi>e</mi><mi>b</mi><mi>a</mi><mi>r</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">sidebar = </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">s</span><span class="mord mathnormal">i</span><span class="mord mathnormal">d</span><span class="mord mathnormal">e</span><span class="mord mathnormal">ba</span><span class="mord mathnormal" style="margin-right:0.02778em;">r</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>('.sidebar'); $sidebar.hide(); // ...stuff... $sidebar.css({ 'background-color': 'pink' }); }
For DOM queries use Cascading
$('.sidebar ul')
or parent > child$('.sidebar > ul')
. jsPerfUse
find
with scoped jQuery object queries.// bad $('.sidebar', 'ul').hide(); // bad $('.sidebar').find('ul').hide(); // good $('.sidebar ul').hide(); // good $('.sidebar > ul').hide(); // good (slower) $sidebar.find('ul'); // good (faster) <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">(</span></span></span></span>sidebar[0]).find('ul');
ECMAScript 5 Compatibility
- Refer to Kangax's ES5 compatibility table
Testing
Yup.
function() { return true; }
Performance
- On Layout & Web Performance
- String vs Array Concat
- Try/Catch Cost In a Loop
- Bang Function
- jQuery Find vs Context, Selector
- innerHTML vs textContent for script text
- Long String Concatenation
- Loading...
Resources
Read This
Other Styleguides
- Google JavaScript Style Guide
- jQuery Core Style Guidelines
- Principles of Writing Consistent, Idiomatic JavaScript
Other Styles
- Naming this in nested functions - Christian Johansen
- Conditional Callbacks
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
Blogs
- DailyJS
- JavaScript Weekly
- JavaScript, JavaScript...
- Bocoup Weblog
- Adequately Good
- NCZOnline
- Perfection Kills
- Ben Alman
- Dmitry Baranovskiy
- Dustin Diaz
- nettuts
In the Wild
This is a list of organizations that are using this style guide. Send us a pull request or open an issue and we'll add you to the list.
- Airbnb: airbnb/javascript
- American Insitutes for Research: AIRAST/javascript
- ExactTarget: ExactTarget/javascript
- GeneralElectric: GeneralElectric/javascript
- GoodData: gooddata/gdc-js-style
- How About We: howaboutwe/javascript
- MinnPost: MinnPost/javascript
- ModCloth: modcloth/javascript
- National Geographic: natgeo/javascript
- Razorfish: razorfish/javascript-style-guide
- Shutterfly: shutterfly/javascript
- Userify: userify/javascript
- Zillow: zillow/javascript
Translation
This style guide is also available in other languages:
- :de: German: timofurrer/javascript-style-guide
- :jp: Japanese: mitsuruog/javacript-style-guide
- :br: Portuguese: armoucar/javascript-style-guide
The JavaScript Style Guide Guide
Contributors
License
(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.
};
```