opentok-style
Advanced tools
A mostly reasonable approach to JavaScript
Primitives: When you access a primitive type you work directly on its value
stringnumberbooleannullundefinedvar 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
objectarrayfunctionvar foo = [1, 2],
bar = foo;
bar[0] = 9;
console.log(foo[0], bar[0]); // => 9, 9
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'
};
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);
...
}
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>';
}
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...
}
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');
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 = createSuperPower();
// good
var superPower = createSuperPower();
Use one var declaration for each variable and declare each variable on a newline.
// bad
var items = getItems(),
goSportsTeam = true,
dragonball = 'z';
// good
var items = getItems();
var goSportsTeam = true;
var dragonball = 'z';
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;
var items = getItems();
var goSportsTeam = true;
// bad
var i, 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;
}
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
Use === and !== over == and !=.
Conditional expressions are evaluated using coercion with the ToBoolean method and always follow these simple rules:
'', otherwise trueif ([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
Use braces with all blocks.
// bad
if (test)
return false;
// bad
if (test) return false;
// good
if (test) {
return false;
}
// bad
function() { return false; }
// good
function() {
return false;
}
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
var active = true; // is current tab
// good
// is current tab
var active = true;
// bad
function getType() {
console.log('fetching type...');
// set the default type to 'no type'
var type = this._type || 'no type';
return type;
}
// good
function getType() {
console.log('fetching type...');
// set the default type to 'no type'
var type = this._type || 'no type';
return type;
}
Prefixing your comments with FIXME or TODO helps other developers quickly understand if you're pointing out a problem that needs to be revisited, or if you're suggesting a solution to the problem that needs to be implemented. These are different than regular comments because they are actionable. The actions are FIXME -- need to figure this out or TODO -- need to implement.
Use // FIXME: to annotate problems
function Calculator() {
// FIXME: shouldn't use a global here
total = 0;
return this;
}
Use // TODO: to annotate solutions to problems
function Calculator() {
// TODO: total should be configurable by an options param
this.total = 0;
return this;
}
**[⬆ 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;
```
- Place an empty newline at the end of the file.
```javascript
// bad
(function(global) {
// ...stuff...
})(this);
```
```javascript
// good
(function(global) {
// ...stuff...
})(this);
```
- Use indentation when making long method chains.
```javascript
// bad
$('#items').find('.selected').highlight().end().find('.open').updateCount();
// good
$('#items')
.find('.selected')
.highlight()
.end()
.find('.open')
.updateCount();
// bad
var leds = stage.selectAll('.led').data(data).enter().append('svg:svg').class('led', true)
.attr('width', (radius + margin) * 2).append('svg:g')
.attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')')
.call(tron.led);
// good
var leds = stage.selectAll('.led')
.data(data)
.enter().append('svg:svg')
.class('led', true)
.attr('width', (radius + margin) * 2)
.append('svg:g')
.attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')')
.call(tron.led);
```
**[⬆ 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
;(function() {
var name = 'Skywalker';
return name;
})();
```
**[⬆ 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.
- **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)
```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;
```
- Booleans:
```javascript
var age = 0;
// bad
var hasAge = new Boolean(age);
// good
var hasAge = Boolean(age);
// good
var hasAge = !!age;
```
**[⬆ back to top](#table-of-contents)**
## 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);
};
}
```
- Name your functions. This is helpful for stack traces.
```javascript
// bad
var log = function(msg) {
console.log(msg);
};
// good
var log = function log(msg) {
console.log(msg);
};
```
**[⬆ back to top](#table-of-contents)**
## Accessors
- Accessor functions for properties are not required
- If you do make accessor functions use val() and val('hello')
```javascript
// bad
dragon.getAge();
// good
dragon.age();
// bad
dragon.setAge(25);
// good
dragon.age(25);
```
- If the property is a boolean, use isVal() or hasVal()
```javascript
// bad
if (!dragon.age()) {
return false;
}
// good
if (!dragon.hasAge()) {
return false;
}
```
**[⬆ back to top](#table-of-contents)**
## Constructors
- Prefer factories over prototypes
```javascript
// bad
function Widget(name) {
this.privateField = 'Hello ';
this.name = name;
}
Widget.prototype.publicMethod = function() {
return this.privateField + this.name + '!';
}
var widget = new Widget('Testing');
// good
var createWidget = function(name) {
var api = new (function Widget(){})();
var privateField = 'Hello ';
api.publicMethod = function() {
return privateField + name + '!';
};
return api;
}
var widget = createWidget('Testing!');
Use prototypes only when an extremely large number of objects will be created (think in the millions)
You're probably better off not using prototype then either.
If you are using it though, 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
var createJedi = function() {
var api = {};
var jumping = false;
var height;
api.jump = function() {
jumping = true;
return true;
};
api.setHeight = function(newHeight) {
height = newHeight;
};
return api;
};
var luke = createJedi();
luke.jump(); // => true
luke.setHeight(20) // => undefined
// good
var createJedi = function() {
var api = {};
var jumping = false;
var height;
api.jump = function() {
jumping = true;
return api;
};
api.setHeight = function(newHeight) {
height = newHeight;
return api;
};
return api;
};
var luke = createJedi();
luke.jump()
.setHeight(20);
It's okay to write a custom toString() method, just make sure it works successfully and causes no side effects.
var createJedi = function(options) {
var api = new (function Jedi() { })();
options || (options = {});
var name = options.name || 'no name';
api.getName = function getName() {
return name;
};
api.toString = function toString() {
return 'Jedi - ' + name;
};
return api;
};
When attaching data payloads to events (whether DOM events, TokBox trigger or node.js EventEmitter), 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
});
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
If your module is adding to the global scope, 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.createFancyInput;
function createFancyInput(options) {
var options = options || {};
}
createFancyInput.noConflict = function noConflict() {
global.createFancyInput = previousFancyInput;
return createFancyInput;
};
global.createFancyInput = createFancyInput;
}(this);
See You Might Not Need jQuery.
Yup.
function() {
return true;
}
Read This
Other Styleguides
Other Styles
Further Reading
Books
Blogs
The list of organizations using similar style guides (including translations) can be found at the original from Airbnb.
(The MIT License)
Copyright (c) 2014 Tokbox Inc. 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.
FAQs
A mostly reasonable approach to JavaScript.
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Research
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