GitHub - mkehlmann/javascript: JavaScript Style Guide
**[[⬆]](#TOC)**
## <a name='whitespace'>Whitespace</a>
- Use soft tabs (spaces) set to 4 spaces
```javascript
// bad (tab)
function() {
var name;
}
// bad (improper number of spaces)
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'
});
```
- Place an empty newline at the end of the file.
```javascript
// bad
(function(global) {
// ...stuff...
})(this);
```
```javascript
// good
(function(global) {
// ...stuff...
})(this);
```
**[[⬆]](#TOC)**
## <a name='commas'>Commas</a>
- Leading commas: **Nope.**
```javascript
// 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'
};
```
- 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'
];
```
**[[⬆]](#TOC)**
## <a name='semicolons'>Semicolons</a>
- **Yup.**
```javascript
// bad
(function() {
var name = 'foo'
return name
})()
// good
(function() {
var name = 'foo';
return name;
})();
// good
;(function() {
var name = 'foo';
return name;
})();
```
**[[⬆]](#TOC)**
## <a name='type-coercion'>Type Casting & Coercion</a>
- 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 = parseInt(inputValue, 10);
```
- Booleans:
```javascript
var age = 0;
// bad
var hasAge = new Boolean(age);
// good
var hasAge = !!age;
```
**[[⬆]](#TOC)**
## <a name='naming-conventions'>Naming Conventions</a>
- 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 = {};
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'
});
```
- When saving a reference to `this` use `_this`.
```javascript
// 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.
```javascript
// bad
var log = function(msg) {
console.log(msg);
};
// good
var log = function log(msg) {
console.log(msg);
};
```
**[[⬆]](#TOC)**
## <a name='modules'>Modules</a>
- Avoid writing inline javascript in HTML or Dust pages whenever possible. Inline javascript is impossible to unit test, is more difficult to debug, and is not our best practice. Instead...
- All scripts should be defined as requirejs modules (http://requirejs.org/docs/api.html#define)
- Here is an example module with a dependency on jQuery
```javascript
// foo.js
define(['jquery'], function($) {
return {
logFooElements: function() {
console.log($('.foo'));
}
};
});
```
This module can then be used as follows
```javascript
// usingFoo.js
require(['foo'], function(foo) {
foo.logFooElements();
});
```
**[[⬆]](#TOC)**
## <a name='htmlcss'>HTML/CSS Interaction</a>
- Use a 'js-' prefix for classes in DOM elements for javascript hooks. This helps us separate javascript classes from CSS classes, thereby helping us avoid breaking javascript when making CSS changes (and vice-versa)
```html
<!-- bad -->
<a class="toggle-widget">Click me!</a>
<!-- If you're using the 'toggle-widget' class for javascript and CSS,
removing this for styling changes will also break javascript -->
<!-- good -->
<a class="js-toggle-widget toggle-widget">Click me!</a>
<!-- Use 'js-toggle-widget' for any javascript code required for this link.
Now you can edit/remove the class 'toggle-widget' for style changes without fear -->
```
**[[⬆]](#TOC)**
## <a name='testing'>Testing</a>
**We use the following for testing**
- [mocha](http://visionmedia.github.io/mocha/) (Framework)
- [chai](http://chaijs.com/) (Assertion Library)
- [blanket](http://blanketjs.org/) (Code Coverage)
Test can be written in either BDD or TDD format, using any of the assertion styles provided by chai (Should, Expect, Assert)
**[[⬆]](#TOC)**
## <a name='performance'>Performance</a>
- [On Layout & Web Performance](http://kellegous.com/j/2013/01/26/layout-performance/)
- [String vs Array Concat](http://jsperf.com/string-vs-array-concat/2)
- [Try/Catch Cost In a Loop](http://jsperf.com/try-catch-in-loop-cost)
- [Bang Function](http://jsperf.com/bang-function)
- [jQuery Find vs Context, Selector](http://jsperf.com/jquery-find-vs-context-sel/13)
- [innerHTML vs textContent for script text](http://jsperf.com/innerhtml-vs-textcontent-for-script-text)
- [Long String Concatenation](http://jsperf.com/ya-string-concat)
**[[⬆]](#TOC)**
## <a name='resources'>Resources</a>
**Read This**
- [Annotated ECMAScript 5.1](http://es5.github.com/)
**Other Styleguides**
- [Google JavaScript Style Guide](http://google-styleguide.googlecode.com/svn/trunk/javascriptguide.xml)
- [jQuery Core Style Guidelines](http://docs.jquery.com/JQuery_Core_Style_Guidelines)
- [Principles of Writing Consistent, Idiomatic JavaScript](https://github.com/rwldrn/idiomatic.js/)
**Other Styles**
- [Naming this in nested functions](https://gist.github.com/4135065) - Christian Johansen
- [Conditional Callbacks](https://github.com/airbnb/javascript/issues/52)
**Further Reading**
- [SuperheroJS](http://superherojs.com/)
- [Front-End Bookmarks](https://github.com/dypsilon/frontend-dev-bookmarks)
- [Understanding JavaScript Closures](http://javascriptweblog.wordpress.com/2010/10/25/understanding-javascript-closures/) - Angus Croll
- [Basic JavaScript for the impatient programmer](http://www.2ality.com/2013/06/basic-javascript.html) - Dr. Axel Rauschmayer
**Books**
- [JavaScript: The Good Parts](http://www.amazon.com/JavaScript-Good-Parts-Douglas-Crockford/dp/0596517742) - Douglas Crockford
- [Eloquent Javascript](http://eloquentjavascript.net/)
- [JavaScript Patterns](http://www.amazon.com/JavaScript-Patterns-Stoyan-Stefanov/dp/0596806752) - Stoyan Stefanov
- [Maintainable JavaScript](http://www.amazon.com/Maintainable-JavaScript-Nicholas-C-Zakas/dp/1449327680) - Nicholas C. Zakas
- [Secrets of the JavaScript Ninja](http://www.amazon.com/Secrets-JavaScript-Ninja-John-Resig/dp/193398869X) - John Resig and Bear Bibeault
- [JSBooks](http://jsbooks.revolunet.com/)
**Blogs**
- [Echo JS](http://echojs.com)
- [DailyJS](http://dailyjs.com/)
- [JavaScript Weekly](http://javascriptweekly.com/)
- [JavaScript, JavaScript...](http://javascriptweblog.wordpress.com/)
- [Bocoup Weblog](http://weblog.bocoup.com/)
- [Adequately Good](http://www.adequatelygood.com/)
- [NCZOnline](http://www.nczonline.net/)
- [Perfection Kills](http://perfectionkills.com/)
- [Ben Alman](http://benalman.com/)
- [Dmitry Baranovskiy](http://dmitry.baranovskiy.com/)
- [Dustin Diaz](http://dustindiaz.com/)
- [nettuts](http://net.tutsplus.com/?s=javascript)
**[[⬆]](#TOC)**
## <a name='license'>License</a>
(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.
**[[⬆]](#TOC)**
# };