Web App Style Guide

A mostly reasonable approach to web application development, derived from the Airbnb and GitHub styleguides.

The short version

Above all else, optimize for readability and maintainability of the code. If you need to do something unusual for the sake of performance or development time, always comment the reasons next to the code in question.

JavaScript

// Always prefer descriptive names over short abbreviations.
var ConstructorName = function (anArray) { // note the space before the bracket
  // two space tabs
  var myVariableName = 'use single quotes', // declare variables first in functions
    myOtherVariable = 1 + (20 + 3), // spaces between operators
    andAnother = []; // semicolons are good

  // White space is good, use lots of white space.
  this._privateProperty = 123; // leading _ for private properties (not variables)

  // Use === and !== over == and !=
  if (andAnother !== undefined) return 42; // no braces ok for single line blocks

  if (1 === 2) { // braces nescessary for multi-line blocks
    return 'Lots and lots of text ' + // max 80 chars per line
      'more and more text';
  }

  return anArray
    .filter(myFilteringFunction) // use indents for long method chains
    .map(myMappingFunction) // prefer array generics over iteration blocks
    .reduce(myReducingFunction);
}

// It's ok to use common short cuts. If a few major libraries use it, it's probably ok.
if (truthy) {}
if (undefinedOrNull == null) {} // will be true
if (collection.length) {} // only enter block if collection has values

CSS (LESS)

/* Write lots of comments to describe style use CSS is notoriously difficult
   to maintain, comments ease the burden.
*/
a {} /* avoid styling html tags directly */

.a-parent-class-name { /* prefer classes over ids */
  color: blue;
  margin: 0; /* don't specify units for zero values */

  .a-child-class-name { /* keep nesting shallow */
  }

  .multiple,
  .classes,
  .multiple-lines {
    margin-bottom: 20px;
  }
}

#IdsArePascalCased {} /* if you do use ids, only have one per rule */

HTML

<!doctype html>
<title>My page title</title>
<h2>Navigation</h2>
<a href="//app.signalfuse.com"> <!-- use lots of spacing and white space to separate blocks -->
  <span class="important">Link</span> <!-- Single lines are ok if they're short -->
</a>
<!-- Avoid unnescessary mark up. The prior three lines should probably be reduced to a
  single one, like <a href="..." class="important">Link</a>.
-->


<!-- No need to close self-closing elements. Also no need to explicitly set unary properties
  such as "disabled" or "required"
-->
<input type="text" disabled>

<!-- prefix directives with sf -->
<!-- when dealing with multiple properties, put them in their own lines -->
<sf-a-directive
  property="value"
  anotherProperty="anotherValue"
/>

Objects

Use the literal syntax for object creation.

// bad
var item = new Object();

// good
var item = {};

Use readable synonyms in place of reserved words.

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

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

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

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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);
  ...
}

Prefer using ES5 iteration functions (forEach, filter, some, all, map, and reduce) over for(;;) loops. Exceptions can be made if performance is an issue.

// bad
var numbers = [1, 2, 3],
    index;

for(index = 0; index < numbers.length; index++){
    doSomethingWithANumber(numbers[index]);
}

// good
var numbers = [1, 2, 3];

numbers.forEach(doSomethingWithANumber);

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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 programmatically 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 = '<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>';
}

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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
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...
}

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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');

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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;
}

Avoid "public private" variables. There's no way to enforce their privacy, so they create a false sense of security which will, eventually, fail.

// bad
function createHero() {
    var man = {};

    man._adjective = 'Dark';
    man.getTitle = function getTagline(){
        return 'The ' + this._adjective + ' Knight';
    };

    return man;
 }

// good
function createHero() {
    var man = {},
        adjective = 'Dark';

    man.getTitle = function getTagline(){
        return 'The ' + adjective + ' Knight';
    };

    return man;
 }

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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
  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

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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
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;
}

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Whitespace

Use soft tabs set to 2 spaces

// 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'
});

Set off operators with spaces.

// bad
var x=y+5;

// good
var x = y + 5;

End files with a single newline character.

// bad
(function (global) {
  // ...stuff...
})(this);

// 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);

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Commas

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'
};

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Semicolons

Yup.

// bad
(function () {
  var name = 'Skywalker'
  return name
})()

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

// good
;(function () {
  var 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
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.

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.
```
// 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:
```
2147483647 >> 0 //=> 2147483647
2147483648 >> 0 //=> -2147483648
2147483649 >> 0 //=> -2147483647
```

Booleans:

var age = 0;

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

// good
var hasAge = Boolean(age);

// good
var 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
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

// 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);
};

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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, 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];
};

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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();
};

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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', 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
});

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Angular

Don't manipulate DOM in Angular Controllers. Use directives when DOM needs to be manipulated.

Don't use global native objects directly, always inject the Angular wrappers; this makes testing much easier.

// bad
function MyController() {
    setTimeout(window.alert('Boop!'));
}

// good
function MyController($window, $setTimeout) {
    $setTimeout($window.alert('Boop!'));
}

List native objects (ones starting with $) first in a function dependency parameter list.

// bad
function MyController(myService, $http) { ... }

// good
function MyController($http, myService) { ... }

Prefix jQuery object variables (such as those returned by angular.element) with a $.

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

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

Cache jQuery lookups.

// 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.

// 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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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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Name		Name	Last commit message	Last commit date
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Web App Style Guide

The short version

JavaScript

CSS (LESS)

HTML

Table of Contents

Objects

Arrays

Strings

Functions

Properties

Variables

Hoisting

Conditional Expressions & Equality

Blocks

Comments

Whitespace

Commas

Semicolons

Type Casting & Coercion

Naming Conventions

Accessors

Constructors

Events

Angular

License

};

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signalfx/web-app-style-guide

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Web App Style Guide

The short version

JavaScript

CSS (LESS)

HTML

Table of Contents

Objects

Arrays

Strings

Functions

Properties

Variables

Hoisting

Conditional Expressions & Equality

Blocks

Comments

Whitespace

Commas

Semicolons

Type Casting & Coercion

Naming Conventions

Accessors

Constructors

Events

Angular

License

};

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