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AngularJS styleguide

Opinionated AngularJS styleguide for teams by @toddmotto

A standardised approach for developing AngularJS applications in teams. This styleguide touches on concepts, syntax, conventions and is based on my experience writing about, talking about, and building Angular applications.

Community

John Papa and I have discussed in-depth styling patterns for Angular and as such have both released separate styleguides. Thanks to those discussions, I've learned some great tips from John that have helped shape this guide. We've both created our own take on a styleguide. I urge you to check his out to compare thoughts.

See the original article that sparked this off

Modules
Controllers
Services and Factory
Directives
Filters
Routing resolves
Publish and subscribe events
Performance
Angular wrapper references
Comment standards
Minification and annotation

Modules

Definitions: Declare modules without a variable using the setter and getter syntax

// avoid
var app = angular.module('app', []);
app.controller();
app.factory();

// recommended
angular
  .module('app', [])
  .controller()
  .factory();

Note: Using angular.module('app', []); sets a module, whereas angular.module('app'); gets the module. Only set once and get for all other instances.

Methods: Pass functions into module methods rather than assign as a callback

// avoid
angular
  .module('app', [])
  .controller('MainCtrl', function MainCtrl () {

  })
  .service('SomeService', function SomeService () {

  });

// recommended
function MainCtrl () {

}
function SomeService () {

}
angular
  .module('app', [])
  .controller('MainCtrl', MainCtrl)
  .service('SomeService', SomeService);

This aids with readability and reduces the volume of code "wrapped" inside the Angular framework

IIFE scoping: To avoid polluting the global scope with our function declarations that get passed into Angular, ensure build tasks wrap the concatenated files inside an IIFE

(function () {

  angular
    .module('app', []);
  
  // MainCtrl.js
  function MainCtrl () {

  }
  
  angular
    .module('app')
    .controller('MainCtrl', MainCtrl);
  
  // SomeService.js
  function SomeService () {

  }
  
  angular
    .module('app')
    .service('SomeService', SomeService);
    
  // ...
    
})();

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Controllers

controllerAs syntax: Controllers are classes, so use the controllerAs syntax at all times

<!-- avoid -->
<div ng-controller="MainCtrl">
  {{ someObject }}
</div>

<!-- recommended -->
<div ng-controller="MainCtrl as vm">
  {{ vm.someObject }}
</div>

In the DOM we get a variable per controller, which aids nested controller methods, avoiding any $parent calls

The controllerAs syntax uses this inside controllers, which gets bound to $scope

// avoid
function MainCtrl ($scope) {
  $scope.someObject = {};
  $scope.doSomething = function () {

  };
}

// recommended
function MainCtrl () {
  this.someObject = {};
  this.doSomething = function () {

  };
}

Only use $scope in controllerAs when necessary; for example, publishing and subscribing events using $emit, $broadcast, $on or $watch. Try to limit the use of these, however, and treat $scope as a special use case

Inheritance: Use prototypal inheritance when extending controller classes

function BaseCtrl () {
  this.doSomething = function () {

  };
}
BaseCtrl.prototype.someObject = {};
BaseCtrl.prototype.sharedSomething = function () {

};

AnotherCtrl.prototype = Object.create(BaseCtrl.prototype);

function AnotherCtrl () {
  this.anotherSomething = function () {

  };
}

Use Object.create with a polyfill for browser support

controllerAs 'vm': Capture the this context of the Controller using vm, standing for ViewModel

// avoid
function MainCtrl () {
  this.doSomething = function () {

  };
}

// recommended
function MainCtrl (SomeService) {
  var vm = this;
  vm.doSomething = SomeService.doSomething;
}

Why? : Function context changes the this value, use it to avoid .bind() calls and scoping issues

Presentational logic only (MVVM): Presentational logic only inside a controller, avoid Business logic (delegate to Services)

// avoid
function MainCtrl () {
  
  var vm = this;

  $http
    .get('/users')
    .success(function (response) {
      vm.users = response;
    });

  vm.removeUser = function (user, index) {
    $http
      .delete('/user/' + user.id)
      .then(function (response) {
        vm.users.splice(index, 1);
      });
  };

}

// recommended
function MainCtrl (UserService) {

  var vm = this;

  UserService
    .getUsers()
    .then(function (response) {
      vm.users = response;
    });

  vm.removeUser = function (user, index) {
    UserService
      .removeUser(user)
      .then(function (response) {
        vm.users.splice(index, 1);
      });
  };

}

Why? : Controllers should fetch Model data from Services, avoiding any Business logic. Controllers should act as a ViewModel and control the data flowing between the Model and the View presentational layer. Business logic in Controllers makes testing Services impossible.

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Services and Factory

All Angular Services are singletons, using .service() or .factory() differs the way Objects are created.

Services: act as a constructor function and are instantiated with the new keyword. Use this for public methods and variables

```javascript
function SomeService () {
  this.someMethod = function () {

  };
}
angular
  .module('app')
  .service('SomeService', SomeService);
```

Factory: Business logic or provider modules, return an Object or closure

Always return a host Object instead of the revealing Module pattern due to the way Object references are bound and updated

function AnotherService () {
  var AnotherService = {};
  AnotherService.someValue = '';
  AnotherService.someMethod = function () {

  };
  return AnotherService;
}
angular
  .module('app')
  .factory('AnotherService', AnotherService);

Why? : Primitive values cannot update alone using the revealing module pattern

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Directives

Declaration restrictions: Only use custom element and custom attribute methods for declaring your Directives ({ restrict: 'EA' }) depending on the Directive's role

<!-- avoid -->

<!-- directive: my-directive -->
<div class="my-directive"></div>

<!-- recommended -->

<my-directive></my-directive>
<div my-directive></div>

Comment and class name declarations are confusing and should be avoided. Comments do not play nicely with older versions of IE. Using an attribute is the safest method for browser coverage.

Templating: Use Array.join('') for clean templating

// avoid
function someDirective () {
  return {
    template: '<div class="some-directive">' +
      '<h1>My directive</h1>' +
    '</div>'
  };
}

// recommended
function someDirective () {
  return {
    template: [
      '<div class="some-directive">',
        '<h1>My directive</h1>',
      '</div>'
    ].join('')
  };
}

Why? : Improves readability as code can be indented properly, it also avoids the + operator which is less clean and can lead to errors if used incorrectly to split lines

DOM manipulation: Takes place only inside Directives, never a controller/service

// avoid
function UploadCtrl () {
  $('.dragzone').on('dragend', function () {
    // handle drop functionality
  });
}
angular
  .module('app')
  .controller('UploadCtrl', UploadCtrl);

// recommended
function dragUpload () {
  return {
    restrict: 'EA',
    link: function (scope, element, attrs) {
      element.on('dragend', function () {
        // handle drop functionality
      });
    }
  };
}
angular
  .module('app')
  .directive('dragUpload', dragUpload);

Naming conventions: Never ng-* prefix custom directives, they might conflict future native directives

// avoid
// <div ng-upload></div>
function ngUpload () {
  return {};
}
angular
  .module('app')
  .directive('ngUpload', ngUpload);

// recommended
// <div drag-upload></div>
function dragUpload () {
  return {};
}
angular
  .module('app')
  .directive('dragUpload', dragUpload);

Directives and Filters are the only providers that have the first letter as lowercase; this is due to strict naming conventions in Directives. Angular hyphenates camelCase, so dragUpload will become <div drag-upload></div> when used on an element.

controllerAs: Use the controllerAs syntax inside Directives as well

// avoid
function dragUpload () {
  return {
    controller: function ($scope) {

    }
  };
}
angular
  .module('app')
  .directive('dragUpload', dragUpload);

// recommended
function dragUpload () {
  return {
    controllerAs: 'vm',
    controller: function () {

    }
  };
}
angular
  .module('app')
  .directive('dragUpload', dragUpload);

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Filters

Global filters: Create global filters using angular.filter() only. Never use local filters inside Controllers/Services

// avoid
function SomeCtrl () {
  this.startsWithLetterA = function (items) {
    return items.filter(function (item) {
      return /^a/i.test(item.name);
    });
  };
}
angular
  .module('app')
  .controller('SomeCtrl', SomeCtrl);

// recommended
function startsWithLetterA () {
  return function (items) {
    return items.filter(function (item) {
      return /^a/i.test(item.name);
    });
  };
}
angular
  .module('app')
  .filter('startsWithLetterA', startsWithLetterA);

This enhances testing and reusability

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Routing resolves

Promises: Resolve Controller dependencies in the $routeProvider (or $stateProvider for ui-router), not the Controller itself

// avoid
function MainCtrl (SomeService) {
  var _this = this;
  // unresolved
  _this.something;
  // resolved asynchronously
  SomeService.doSomething().then(function (response) {
    _this.something = response;
  });
}
angular
  .module('app')
  .controller('MainCtrl', MainCtrl);

// recommended
function config ($routeProvider) {
  $routeProvider
  .when('/', {
    templateUrl: 'views/main.html',
    resolve: {
      // resolve here
    }
  });
}
angular
  .module('app')
  .config(config);

Controller.resolve property: Never bind logic to the router itself. Reference a resolve property for each Controller to couple the logic

// avoid
function MainCtrl (SomeService) {
  this.something = SomeService.something;
}

function config ($routeProvider) {
  $routeProvider
  .when('/', {
    templateUrl: 'views/main.html',
    controllerAs: 'vm',
    controller: 'MainCtrl'
    resolve: {
      doSomething: function () {
        return SomeService.doSomething();
      }
    }
  });
}

// recommended
function MainCtrl (SomeService) {
  this.something = SomeService.something;
}

MainCtrl.resolve = {
  doSomething: function (SomeService) {
    return SomeService.doSomething();
  }
};

function config ($routeProvider) {
  $routeProvider
  .when('/', {
    templateUrl: 'views/main.html',
    controllerAs: 'vm',
    controller: 'MainCtrl'
    resolve: MainCtrl.resolve
  });
}

This keeps resolve dependencies inside the same file as the Controller and the router free from logic

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Publish and subscribe events

$scope: Use the $emit and $broadcast methods to trigger events to direct relationship scopes only

// up the $scope
$scope.$emit('customEvent', data);

// down the $scope
$scope.$broadcast('customEvent', data);

$rootScope: Use only $emit as an application-wide event bus and remember to unbind listeners
```
// all $rootScope.$on listeners
$rootScope.$emit('customEvent', data);
```
Hint: Because the $rootScope is never destroyed, $rootScope.$on listeners aren't either, unlike $scope.$on listeners and will always persist, so they need destroying when the relevant $scope fires the $destroy event
```
// call the closure
var unbind = $rootScope.$on('customEvent'[, callback]);
$scope.$on('$destroy', unbind);
```

For multiple $rootScope listeners, use an Object literal and loop each one on the $destroy event to unbind all automatically

var rootListeners = {
  'customEvent1': $rootScope.$on('customEvent1'[, callback]),
  'customEvent2': $rootScope.$on('customEvent2'[, callback]),
  'customEvent3': $rootScope.$on('customEvent3'[, callback])
};
for (var unbind in rootListeners) {
  $scope.$on('$destroy', rootListeners[unbind]);
}

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Performance

One-time binding syntax: In newer versions of Angular (v1.3.0-beta.10+), use the one-time binding syntax {{ ::value }} where it makes sense
```
// avoid
<h1>{{ vm.title }}</h1>

// recommended
<h1>{{ ::vm.title }}</h1>
```
Why? : Binding once removes the watcher from the scope's $$watchers array after the undefined variable becomes resolved, thus improving performance in each dirty-check
Consider $scope.$digest: Use $scope.$digest over $scope.$apply where it makes sense. Only child scopes will update
```
$scope.$digest();
```
Why? : $scope.$apply will call $rootScope.$digest, which causes the entire application $$watchers to dirty-check again. Using $scope.$digest will dirty check current and child scopes from the initiated $scope

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Angular wrapper references

$document and $window: Use $document and $window at all times to aid testing and Angular references

// avoid
function dragUpload () {
  return {
    link: function ($scope, $element, $attrs) {
      document.addEventListener('click', function () {

      });
    }
  };
}

// recommended
function dragUpload () {
  return {
    link: function ($scope, $element, $attrs, $document) {
      $document.addEventListener('click', function () {

      });
    }
  };
}

$timeout and $interval: Use $timeout and $interval over their native counterparts to keep Angular's two-way data binding up to date

// avoid
function dragUpload () {
  return {
    link: function ($scope, $element, $attrs) {
      setTimeout(function () {
        //
      }, 1000);
    }
  };
}

// recommended
function dragUpload ($timeout) {
  return {
    link: function ($scope, $element, $attrs) {
      $timeout(function () {
        //
      }, 1000);
    }
  };
}

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Comment standards

jsDoc: Use jsDoc syntax to document function names, description, params and returns

/**
 * @name SomeService
 * @desc Main application Controller
 */
function SomeService (SomeService) {

  /**
   * @name doSomething
   * @desc Does something awesome
   * @param {Number} x - First number to do something with
   * @param {Number} y - Second number to do something with
   * @returns {Number}
   */
  this.doSomething = function (x, y) {
    return x * y;
  };

}
angular
  .module('app')
  .service('SomeService', SomeService);

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Minification and annotation

ng-annotate: Use ng-annotate for Gulp as ng-min is deprecated, and comment functions that need automated dependency injection using /** @ngInject */

/**
 * @ngInject
 */
function MainCtrl (SomeService) {
  this.doSomething = SomeService.doSomething;
}
angular
  .module('app')
  .controller('MainCtrl', MainCtrl);

Which produces the following output with the $inject annotation

/**
 * @ngInject
 */
function MainCtrl (SomeService) {
  this.doSomething = SomeService.doSomething;
}
MainCtrl.$inject = ['SomeService'];
angular
  .module('app')
  .controller('MainCtrl', MainCtrl);

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Angular docs

For anything else, including API reference, check the Angular documentation.

Contributing

Open an issue first to discuss potential changes/additions.

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.

Awesome

AngularJS styleguide

Community

Table of Contents

Modules

Controllers

Services and Factory

Directives

Filters

Routing resolves

Publish and subscribe events

Performance

Angular wrapper references

Comment standards

Minification and annotation

Angular docs

Contributing

License

(The MIT License)