AngularJS styleguide

Opinionated AngularJS styleguide for teams by @toddmotto

From my experience with Angular, several talks and working in teams, here's my opinionated styleguide for syntax, building and structuring Angular applications.

See the original article

Table of Contents

1. Modules
2. Controllers
3. Services
4. Factory
5. Directives
6. Filters
7. Routing resolves
8. Publish and subscribe events
9. Angular wrapper references
10. Comment standards
11. Minification and annotation

Modules

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

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

  // bad
  angular
    .module('app', [])
    .controller('MainCtrl', function MainCtrl () {
  
    })
    .service('SomeService', function SomeService () {
  
    });
  
  // good
  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 which 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

  <!-- bad -->
  <div ng-controller="MainCtrl">
    {{ someObject }}
  </div>
  
  <!-- good -->
  <div ng-controller="MainCtrl as main">
    {{ main.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

  // bad
  function MainCtrl ($scope) {
    $scope.someObject = {};
    $scope.doSomething = function () {
  
    };
  }
  
  // good
  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 using $watch, try to limit the use of these, however and treat $scope uses as special

• 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

• Zero-logic: No logic inside a controller, delegate to services

  // bad
  function MainCtrl () {
    this.doSomething = function () {
  
    };
  }
  
  // good
  function MainCtrl (SomeService) {
    this.doSomething = SomeService.doSomething;
  }

• Think "skinny controller, fat service"

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Services

• Services are classes and are instantiated with the new keyword, use this for public methods and variables

  function SomeService () {
    this.someMethod = function () {
  
    };
  }

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Factory

• Singletons: Factories are singletons, return a host Object inside each Factory to avoid primitive binding issues

  // bad
  function AnotherService () {
    var someValue = '';
    var someMethod = function () {
  
    };
    return {
      someValue: someValue,
      someMethod: someMethod
    };
  }
  
  // good
  function AnotherService () {
    var AnotherService = {};
    AnotherService.someValue = '';
    AnotherService.someMethod = function () {
  
    };
    return AnotherService;
  }

• This way bindings are mirrored across the host Object, 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

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

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

• DOM manipulation: Only takes place inside Directives, never a controller/service

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

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

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

• controllerAs: Use the controllerAs syntax inside Directives also

  // bad
  function dragUpload () {
    return {
      controller: function ($scope) {
  
      }
    };
  }
  angular
    .module('app')
    .directive('dragUpload', dragUpload);
  
  // good
  function dragUpload () {
    return {
      controllerAs: 'dragUpload',
      controller: function () {
  
      }
    };
  }
  angular
    .module('app')
    .directive('dragUpload', dragUpload);

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Filters

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

  // bad
  function SomeCtrl () {
    this.startsWithLetterA = function (items) {
      return items.filter(function (item) {
        return /$a/i.test(item.name);
      });
    };
  }
  angular
    .module('app')
    .controller('SomeCtrl', SomeCtrl);
  
  // good
  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 dependencies of a Controller in the $routeProvider (or $stateProvider for ui-router) not the Controller itself

  // bad
  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);
  
  // good
  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

  // bad
  function MainCtrl (SomeService) {
    this.something = SomeService.something;
  }
  
  function config ($routeProvider) {
    $routeProvider
    .when('/', {
      templateUrl: 'views/main.html',
      controllerAs: 'main',
      controller: 'MainCtrl'
      resolve: {
        doSomething: function () {
          return SomeService.doSomething();
        }
      }
    });
  }
  
  // good
  function MainCtrl (SomeService) {
    this.something = SomeService.something;
  }
  
  MainCtrl.resolve = {
    doSomething: function () {
      return SomeService.doSomething();
    }
  };
  
  function config ($routeProvider) {
    $routeProvider
    .when('/', {
      templateUrl: 'views/main.html',
      controllerAs: 'main',
      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: $rootScope.$on listeners are different to $scope.$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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Angular wrapper references

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

  // bad
  function dragUpload () {
    return {
      link: function (scope, element, attrs) {
        document.addEventListener('click', function () {
  
        });
      }
    };
  }
  
  // good
  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

  // bad
  function dragUpload () {
    return {
      link: function (scope, element, attrs) {
        setTimeout(function () {
          //
        }, 1000);
      }
    };
  }
  
  // good
  function dragUpload () {
    return {
      link: function (scope, element, attrs, $timeout) {
        $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, API reference, check the Angular documentation.

Contributing

Open an issue first to discuss potential changes/additions.

License

(The MIT License)

Copyright (c) 2014 Todd Motto

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.