angularjs-style-guide: A repository from ckrad

#Introduction

The goal of this style guide is to present a set of best practices and style guidelines for one AngularJS application. These best practices are collected from:

AngularJS source code
Source code or articles I've read
My own experience

Note: this is still a draft of the style guide, its main goal is to be community-driven so filling the gaps will be greatly appreciated by the whole community.

In this style guide you won't find common guidelines for JavaScript development. Such can be found at:

For AngularJS development recommended is the Google's JavaScript style guide.

In AngularJS's GitHub wiki there is a similar section by ProLoser, you can check it here.

#Table of content

General
Modules
Controllers
Directives
Filters
Services
Templates
Routing
Testing
Contribution

#General

Directory structure

Since a large AngularJS application has many components it's best to structure them in a directory hierarchy. There are two main approaches:

Creating high-level divisions by component types and lower-level divisions by functionality.

In this way the directory structure will look like:

.
├── app
│   ├── app.js
│   ├── controllers
│   │   ├── page1
│   │   │   ├── FirstCtrl.js
│   │   │   └── SecondCtrl.js
│   │   └── page2
│   │       └── ThirdCtrl.js
│   ├── directives
│   │   ├── page1
│   │   │   └── directive1.js
│   │   └── page2
│   │       ├── directive2.js
│   │       └── directive3.js
│   ├── filters
│   │   ├── page1
│   │   └── page2
│   └── services
│       ├── CommonService.js
│       ├── cache
│       │   ├── Cache1.js
│       │   └── Cache2.js
│       └── models
│           ├── Model1.js
│           └── Model2.js
├── lib
└── test

Creating high-level divisions by functionality and lower-level divisions by component types.

Here is its layout:

.
├── app
│   ├── app.js
│   ├── common
│   │   ├── controllers
│   │   ├── directives
│   │   ├── filters
│   │   └── services
│   ├── page1
│   │   ├── controllers
│   │   │   ├── FirstCtrl.js
│   │   │   └── SecondCtrl.js
│   │   ├── directives
│   │   │   └── directive1.js
│   │   ├── filters
│   │   │   ├── filter1.js
│   │   │   └── filter2.js
│   │   └── services
│   │       ├── service1.js
│   │       └── service2.js
│   └── page2
│       ├── controllers
│       │   └── ThirdCtrl.js
│       ├── directives
│       │   ├── directive2.js
│       │   └── directive3.js
│       ├── filters
│       │   └── filter3.js
│       └── services
│           └── service3.js
├── lib
└── test

When creating directives it may be useful to put all the files associated with the given directive files (i.e. templates, CSS/SASS files, JavaScript) in a single folder. If you choose to use this style be consistent and use it everywhere along your project.

app
└── directives
    ├── directive1
    │   ├── directive1.html
    │   ├── directive1.js
    │   └── directive1.sass
    └── directive2
        ├── directive2.html
        ├── directive2.js
        └── directive2.sass

This approach can be combined with both directory structures above.

One more slight variation of both directory structures is the one used in ng-boilerplate. In it, the unit tests for a given component are put in the folder where the component is located. This way when you make changes to a given component finding its test is easy. The tests also act as documentation and show uses cases.

services
├── cache
│   ├── cache1.js
│   └── cache1.spec.js
└── models
    ├── model1.js
    └── model1.spec.js

The app.js file contains route definitions, configuration and/or manual bootstrap (if required).
Each JavaScript file should only hold a single component. The file should be named with the component's name.
Use Angular project structure template like Yeoman, ng-boilerplate.

I prefer the first structure because it makes common components easier to find.

Conventions about component naming can be found in each component section.

Optimize the digest cycle

Watch only the most vital variables (for example: when using real-time communication, don't cause a digest loop in each received message).
Make computations in $watch as simple as possible. Making heavy and slow computations in a single $watch will slow down the whole application (the $digest loop is done in a single thread because of the single-threaded nature of JavaScript).
Set third parameter in $timeout function to false to skip digest loop when no watched variables are impacted by the invocation of the $timeout callback function.

Others

Use:
- $timeout instead of setTimeout
- $interval instead of setInterval
- $window instead of window
- $document instead of document
- $http instead of $.ajax

This will make your testing easier and in some cases prevent unexpected behaviour (for example, if you missed $scope.$apply in setTimeout).

Automate your workflow using tools like:
- Yeoman
- Grunt
- Bower
Use promises ($q) instead of callbacks. It will make your code look more elegant and clean, and save you from callback hell.
Use $resource instead of $http when possible. The higher level of abstraction will save you from redundancy.
Use an AngularJS pre-minifier (like ngmin or ng-annotate) for preventing problems after minification.
Don't use globals. Resolve all dependencies using Dependency Injection.
Do not pollute your $scope. Only add functions and variables that are being used in the templates.
Prefer the usage of controllers instead of ngInit. The only appropriate use of ngInit is for aliasing special properties of ngRepeat. Besides this case, you should use controllers rather than ngInit to initialize values on a scope.
Do not use $ prefix for the names of variables, properties and methods. This prefix is reserved for AngularJS usage.

#Modules

Modules should be named with lowerCamelCase. For indicating that module b is submodule of module a you can nest them by using namespacing like: a.b.

There are two common ways for structuring the modules:

By functionality
By component type

Currently there's not a big difference, but the first way looks cleaner. Also, if lazy-loading modules is implemented (currently not in the AngularJS roadmap), it will improve the app's performance.

#Controllers

Do not manipulate DOM in your controllers, this will make your controllers harder for testing and will violate the Separation of Concerns principle. Use directives instead.
The naming of the controller is done using the controller's functionality (for example shopping cart, homepage, admin panel) and the substring Ctrl in the end. The controllers are named UpperCamelCase (HomePageCtrl, ShoppingCartCtrl, AdminPanelCtrl, etc.).
The controllers should not be defined as globals (no matter AngularJS allows this, it is a bad practice to pollute the global namespace).
Use array syntax for controller definitions:

module.controller('MyCtrl', ['dependency1', 'dependency2', ..., 'dependencyn', function (dependency1, dependency2, ..., dependencyn) {
  //...body
}]);

Using this type of definition avoids problems with minification. You can automatically generate the array definition from standard one using tools like ng-annotate (and grunt task grunt-ng-annotate).

Use the original names of the controller's dependencies. This will help you produce more readable code:

module.controller('MyCtrl', ['$scope', function (s) {
  //...body
}]);

is less readable than:

module.controller('MyCtrl', ['$scope', function ($scope) {
  //...body
}]);

This especially applies to a file that has so much code that you'd need to scroll through. This would possibly cause you to forget which variable is tied to which dependency.

Make the controllers as lean as possible. Abstract commonly used functions into a service.
Communicate within different controllers using method invocation (possible when children wants to communicate with parent) or $emit, $broadcast and $on methods. The emitted and broadcasted messages should be kept to a minimum.
Make a list of all messages which are passed using $emit, $broadcast and manage it carefully because of name collisions and possible bugs.
When you need to format data encapsulate the formatting logic into a filter and declare it as dependency:

module.filter('myFormat', function () {
  return function () {
    //body...
  };
});

module.controller('MyCtrl', ['$scope', 'myFormatFilter', function ($scope, myFormatFilter) {
  //body...
}]);

#Directives

Name your directives with lowerCamelCase
Use scope instead of $scope in your link function. In the compile, post/pre link functions you have already defined arguments which will be passed when the function is invoked, you won't be able to change them using DI. This style is also used in AngularJS's source code.
Use custom prefixes for your directives to prevent name collisions with third-party libraries.
Do not use ng or ui prefixes since they are reserved for AngularJS and AngularJS UI usage.
DOM manipulations must be done only through directives.
Create an isolated scope when you develop reusable components.
Use directives as attributes or elements instead of comments or classes, this will make your code more readable.
Use $scope.$on('$destroy', fn) for cleaning up. This is especially useful when you're wrapping third-party plugins as directives.
Do not forget to use $sce when you should deal with untrusted content.

#Filters

Name your filters with lowerCamelCase
Make your filters as light as possible. They are called often during the $digest loop so creating a slow filter will slow down your app.

#Services

Use camelCase (lower or upper) to name your services.
Encapsulate business logic in services.
Services representing the domain preferably a service instead of a factory. In this way we can take advantage of the "klassical" inheritance easier:

function Human() {
  //body
}
Human.prototype.talk = function () {
  return "I'm talking";
};

function Developer() {
  //body
}
Developer.prototype = Object.create(Human.prototype);
Developer.prototype.code = function () {
  return "I'm coding";
};

myModule.service('Human', Human);
myModule.service('Developer', Developer);

For session-level cache you can use $cacheFactory. This should be used to cache results from requests or heavy computations.

#Templates

Use ng-bind or ng-cloak instead of simple {{ }} to prevent flashing content.
Avoid writing complex code in the template.
When you need to set the src of an image dynamically use ng-src instead of src with {{}} template.
Instead of using scope variable as string and using it with style attribute with {{ }}, use the directive ng-style with object-like parameters and scope variables as values:

<script>
...
$scope.divStyle = {
  width: 200,
  position: 'relative'
};
...
</script>

<div ng-style="divStyle">my beautifully styled div which will work in IE</div>;

#Routing

Use resolve to resolve dependencies before the view is shown.

#Testing

TBD

Until it is completed you can use this one.

#Contribution

Since the goal of this style guide is to be community-driven, contributions are greatly appriciated. For example, you can contribute by extending the Testing section or by translating the style guide to your language.

ckrad/angularjs-style-guide

Directory structure

Optimize the digest cycle

Others