sethdford / angularjs-style-guide

AngularJS style guide used at GoCardless

Angular Style Guide

Table of Contents

1. High-level Goals
2. Directory and File Structure
3. Parts of Angular
4. General Patterns and Anti-patterns

High-level Goals

The principles we use to guide low-level decision making are:

1. Prioritise readability.
2. Be explicit, not implicit.
3. Favour composability over inheritance.
4. Think forward – ES6 and Web Components (Angular 2.0).
5. Know when to deviate from the style guide.

Directory and File Structure

We organise our code as follows:

Folder structure

/app
  /components
    /alert
      alert.directive.js
      alert.directive.spec.js
      alert.template.html
  /config
    main.config.js
  /constants
    api-url.constant.js
  /routes
    /customers
      /index
        customers-index.template.html
        customers-index.route.js
        customers-index.controller.js
        customers-index.e2e.js
  /helpers
    /currency
      currency-filter.js
      currency-filter.spec.js
    /unit
    /e2e
  /services
    /creditors
      creditors.js
      creditors.spec.js
  bootstrap.js
  main.js
/assets
  /fonts
  /images
  /stylesheets
404.html
index.html

Specs (Unit/E2E)

Keep spec files in the same folder as the code being tested.

Components

Components are encapsulated DOM components. Each component contains all the HTML, CSS, JavaScript, and other dependencies needed to render itself.

Routes

A view, made up of components and unique pieces of UI, that points to a URL. Like components, each route contains all the HTML, CSS, JavaScript, and other dependencies needed to render itself.

Services

Services contain Business logic. For example, $http abstractions.

Config

Configures Providers. For example, $locationProvider.html5Mode(true);.

Constants

Constant variables. For example, export var API = 'https://api.gocardless.com';. Although JavaScript does not yet support constants, naming a variable in all uppercase is a convention that denotes the variable should not be mutated.

Helpers

Pure functions. For example, a currencyFilter might take in a number and format it for a certain currency. Helpers take input and return output without having any side effects.

Parts of Angular

Rules for using each of the core parts of AngularJS (routes, directives, controllers, modules, and templates).

Routes

Use resolvers to inject data.

Why: The page is rendered only when all data is available, which means you don't get any views being rendered without data.

// Recommended
$stateProvider.state('customers.show', {
  url: '/customers/:id',
  template: template,
  controller: 'CustomersShowController',
  controllerAs: 'ctrl',
  resolve: {
    customer: [
      'Customers',
      '$stateParams',
      function customerResolver(Customers, $stateParams) {
        return Customers.findOne({
          params: { id: $stateParams.id }
        });
      }
    ]
  }
});

// Avoid
// Note: Controller written inline for the example
$stateProvider.state('customers.show', {
  url: '/customers/:id',
  template: template,
  controllerAs: 'ctrl',
  controller: [
    'Customers',
    '$stateParams',
    function CustomersShowController(Customers, $stateParams) {
      var ctrl = this;
      Customers.findOne({
        params: { id: $stateParams.id }
      }).then(function(customers) {
        ctrl.customers = customers;
      });
    }
  ]
});

Use query parameters to store route state. For example, the current offset and limit when paginating.

Why: The current view should be accurately reflected in the URL, which means any page refresh puts the user back in the exact state they were in.

// Recommended
function nextPage() {
  var currentOffset = parseInt($stateParams.offset, 10) || 0;
  var limit = parseInt($stateParams.limit, 10) || 10;
  var nextOffset = currentOffset + limit;
  Payments.findAll({
    params: { customers: $stateParams.id, limit: limit, offset: nextOffset }
  });
}

// Avoid
// Keeping route state in memory only
var currentOffset = 0;
var limit = 10;

function nextPage() {
  var nextOffset = currentOffset + limit;
  currentOffset = nextOffset;
  Payments.findAll({
    params: { customers: $stateParams.id, limit: limit, offset: nextOffset }
  });
}

Directives

Use element directives when content is injected, else use attribute directives.

Why: Separates responsibility: element directives add content; attribute directives add behaviour; class attributes add style.

<!-- Recommended -->
<alert message="Error" />
<!-- Replaced with: -->
<div class="alert">
  <span class="alert__message">Error</span>
</div>

<!-- Avoid -->
<p alert message="Error">
</p>
<!-- Replaced with: -->
<p alert message="Error">
  <div class="alert">
    <span class="alert__message">Error</span>
  </div>
</p>

<!-- Recommended -->
<button prevent-default="click">Submit</button>

<!-- Avoid -->
<prevent-default event="click">Submit</prevent-default>

Use an isolate scope for element directives. Use inherited scope for attribute directives.

Why: Using an isolate scope forces you to expose an API by giving the component all the data it needs. This increases reusability and testability. Attribute directives should not have an isolate scope because doing so overwrites the current scope.

// Recommended
angular.module('AlertListComponentModule', [])
  .directive('alertList', [
    function alertListDirective() {
      return {
        restrict: 'E',
        scope: {}
      };
    }
  ]);

// Avoid
angular.module('AlertListComponentModule', [])
  .directive('alertList', [
    function alertListDirective() {
      return {
        restrict: 'E'
      };
    }
  ]);

// Recommended
angular.module('AlertListComponentModule', [])
  .directive('alertList', [
    function alertListDirective() {
      return {
        restrict: 'A',
        scope: true
      };
    }
  ]);

// Avoid
angular.module('AlertListComponentModule', [])
  .directive('alertList', [
    function alertListDirective() {
      return {
        restrict: 'A'
      };
    }
  ]);

When using isolate-scope properties, always bindToController.

Why: It explicitly shows what variables are shared via the controller.

// Recommended
angular.module('AlertListComponentModule', [])
  .directive('alertList', [
    function alertListDirective() {
      return {
        restrict: 'E',
        controller: 'AlertListController',
        controllerAs: 'ctrl',
        bindToController: true,
        template: template,
        replace: true,
        scope: {}
      };
    }
  ]);

// Avoid
angular.module('AlertListComponentModule', [])
  .directive('alertList', [
    function alertListDirective() {
      return {
        restrict: 'E',
        controller: 'AlertListController',
        template: template,
        replace: true,
        scope: {}
      };
    }
  ]);

Tear down directives, subscribe to $scope.$on('$destroy', ...) to get rid of any event listeners or DOM nodes created outside the directive element.

Why: It avoids memory leaks and duplicate event listeners being bound when the directive is re-created.

// Recommended
angular.module('AdminExpandComponentModule', [])
  .directive('adminExpand', [
    '$window',
    function adminExpand($window) {
      return {
        restrict: 'A',
        scope: {},
        link: function adminExpandLink(scope, element) {
          function expand() {
            element.addClass('is-expanded');
          }

          $window.document.addEventListener('click', expand);

          scope.$on('$destroy', function onAdminExpandDestroy() {
            $window.document.removeEventListener('click', expand);
          });
        }
      };
    }
  ]);

// Avoid
angular.module('AdminExpandComponentModule', [])
  .directive('adminExpand', [
    '$window',
    function adminExpand($window) {
      return {
        restrict: 'A',
        scope: {},
        link: function adminExpandLink(scope, element) {
          function expand() {
            element.addClass('is-expanded');
          }

          $window.document.addEventListener('click', expand);
        }
      };
    }
  ]);

Anti-Patterns

• Don't rely on jQuery selectors. Use directives to target elements instead.
• Don't use jQuery to generate templates or DOM. Use directive templates instead.

Controllers

Use controllerAs syntax.

Why: It explicitly shows what controller a variable belongs to, by writing {{ ctrl.foo }} instead of {{ foo }}.

// Recommended
$stateProvider.state('authRequired.customers.show', {
  url: '/customers/:id',
  template: template,
  controller: 'CustomersShowController',
  controllerAs: 'ctrl'
});

// Avoid
$stateProvider.state('authRequired.customers.show', {
  url: '/customers/:id',
  template: template,
  controller: 'CustomersShowController'
});

// Recommended
angular.module('AlertListComponentModule', [])
  .directive('alertList', [
    function alertListDirective() {
      return {
        restrict: 'E',
        controller: 'AlertListController',
        controllerAs: 'ctrl',
        bindToController: true,
        template: template,
        replace: true,
        scope: {}
      };
    }
  ]);

// Avoid
angular.module('AlertListComponentModule', [])
  .directive('alertList', [
    function alertListDirective() {
      return {
        restrict: 'E',
        controller: 'AlertListController',
        template: template,
        replace: true,
        scope: {}
      };
    }
  ]);

Inject ready data instead of loading it in the controller.

Why:

• 2.1. Simplifies testing with mock data.
• 2.2. Separates concerns: data is resolved in the route and used in the controller.

// Recommended
angular.module('CustomersShowControllerModule', [])
  .controller('CustomersShowController', [
    'customer', 'payments', 'mandates',
    function CustomersShowController(customer, payments, mandates){
      var ctrl = this;

      _.extend(ctrl, {
        customer: customer,
        payments: payments,
        mandates: mandates
      });
    }
  ]);

// Avoid
angular.module('CustomersShowControllerModule', [])
  .controller('CustomersShowController', [
    'Customers', 'Payments', 'Mandates',
    function CustomersShowController(Customers, Payments, Mandates){
      var ctrl = this;

      Customers.findOne({
        params: { id: $stateParams.id }
      }).then(function(customers) {
        ctrl.customers = customers;
      });

      Payments.findAll().then(function(payments) {
        ctrl.payments = payments;
      });

      Mandates.findAll().then(function(mandates) {
        ctrl.mandates = mandates;
      });
    }
  ]);

Extend a controller’s properties onto the controller.

Why: What is being exported is clear and always done in one place, at the bottom of the file.

// Recommended
angular.module('OrganisationRolesNewControllerModule', [])
  .controller('OrganisationRolesNewController', [
    'permissions',
    function CustomersShowController(permissions){
      var ctrl = this;

      function setAllPermissions(access) {
        ctrl.form.permissions.forEach(function(permission) {
          permission.access = access;
        });
      }

      _.extend(ctrl, {
        permissions: permissions,
        setAllPermissions: setAllPermissions
      });
    }
  ]);

// Avoid
angular.module('OrganisationRolesNewControllerModule', [])
  .controller('OrganisationRolesNewController', [
    'permissions',
    function CustomersShowController(permissions){
      var ctrl = this;

      ctrl.permissions = permissions;

      ctrl.setAllPermissions = function setAllPermissions(access) {
        ctrl.form.permissions.forEach(function(permission) {
          permission.access = access;
        });
      }
    }
  ]);

Only extend the controller with properties used in templates.

Why: Adding unused properties to the digest cycle is expensive.

// Recommended
angular.module('WebhooksIndexControllerModule', [])
  .controller('WebhooksIndexController', [
    'TestWebhooks', 'AlertList', 'webhooks'
    function WebhooksIndexController(TestWebhooks, AlertList, webhooks) {
      var ctrl = this;

      function success() {
        AlertList.success('Your test webhook has been created and will be sent shortly');
      }

      function error() {
        AlertList.error('Failed to send test webhook, please try again');
      }

      function sendTestWebhook(webhook) {
        TestWebhooks.create({
          data: { test_webhooks: webhook }
        }).then(success, error);
      }

      _.extend(ctrl, {
        webhooks: webhooks,
        sendTestWebhook: sendTestWebhook
      });
    }
  ]);

// Avoid
angular.module('WebhooksIndexControllerModule', [])
  .controller('WebhooksIndexController', [
    'TestWebhooks', 'AlertList', 'webhooks'
    function WebhooksIndexController(TestWebhooks, AlertList, webhooks) {
      var ctrl = this;

      function success() {
        AlertList.success('Your test webhook has been created and will be sent shortly');
      }

      function error() {
        AlertList.error('Failed to send test webhook, please try again');
      }

      function sendTestWebhook(webhook) {
        TestWebhooks.create({
          data: { test_webhooks: webhook }
        }).then(success, error);
      }

      _.extend(ctrl, {
        webhooks: webhooks,
        success: success,
        error: error,
        sendTestWebhook: sendTestWebhook
      });
    }
  ]);

Store presentation logic in controllers and business logic in services.

Why:

• 5.1. Simplifies testing business logic.
• 5.2. Controllers are glue code, and therefore require integration tests, not unit tests.

// Recommended
angular.module('WebhooksControllerModule', [])
.controller('WebhooksController', [
  'TestWebhooks',
  function WebhooksController(TestWebhooks) {
    var ctrl = this;

    function sendTestWebhook(webhook) {
      TestWebhooks.create({
        data: { test_webhooks: webhook }
      }).then(function() {
        $state.go('authRequired.organisation.roles.index', null);
        AlertList.success('Your test webhook has been created and will be sent shortly');
      });
    }

    _.extend(ctrl, {
      sendTestWebhook: sendTestWebhook
    });
  }
]);

// Avoid
angular.module('WebhooksControllerModule', [])
.controller('WebhooksController', [
  '$http',
  function WebhooksController($http) {
    var ctrl = this;

    function sendTestWebhook(webhook) {
      $http({
        method: 'POST',
        data: { test_webhooks: webhook },
        url: '/test_webhooks'
      });
    }

    _.extend(ctrl, {
      sendTestWebhook: sendTestWebhook
    });
  }
]);

Only instantiate controllers through routes or directives.

Why: Allows reuse of controllers and encourages component encapsulation.

// Recommended
angular.module('AlertListComponentModule', [])
  .directive('alertList', [
    function alertListDirective() {
      return {
        restrict: 'E',
        controller: 'AlertListController',
        controllerAs: 'ctrl',
        bindToController: true,
        template: template,
        replace: true,
        scope: {}
      };
    }
  ]);

<!-- Avoid -->
<div ng-controller='AlertListController as ctrl'>
  <span>{{ ctrl.message }}</span>
</div>

Anti-Patterns

• Don’t manipulate DOM in your controllers, this will make them harder to test. Use directives instead.

Modules

Create one module per file and don’t alter a module other than where it is defined.

Why:

• 1.1. Prevents polluting the global scope.
• 1.2. Simplifies unit testing by declaring all dependencies needed to run each module.
• 1.3. Negates necessity to load files in a specific order.

// Recommended
angular.module('UsersPasswordEditControllerModule', [])
  .controller('UsersPasswordEditController', []);

// Avoid
angular.module('app')
  .controller('UsersPasswordEditController', []);

Use ES6 module system and reference other modules using Angular Module’s name property.

Why:

• 2.1. Encapsulates all required files, making unit testing easier and error feedback more specific.
• 2.2. Simplifies upgrading to Angular 2.0, which uses ES6 modules.

// Recommended
import {PasswordResetTokensModule} from 'app/services/password-reset-tokens/password-reset-tokens';
import {SessionModule} from 'app/services/session/session';
import {AlertListModule} from 'app/components/alert-list/alert-list';

export var UsersPasswordEditControllerModule = angular.module('UsersPasswordEditControllerModule', [
  PasswordResetTokensModule.name,
  SessionModule.name,
  AlertListModule.name
]);

// Avoid
import {PasswordResetTokensModule} from 'app/services/password-reset-tokens/password-reset-tokens';
import {SessionModule} from 'app/services/session/session';
import {AlertListModule} from 'app/components/alert-list/alert-list';

export var UsersPasswordEditControllerModule = angular.module('UsersPasswordEditControllerModule', [
  'PasswordResetTokensModule',
  'SessionModule',
  'AlertListModule'
]);

Use relative imports only when importing from the current directory or any of its children. Use absolute paths when referencing modules in parent directories.

Why: Makes it easier to edit directories.

// Current directory: app/services/creditors/

// Recommended
import {API_URL} from 'app/constants/api-url.constant';
import {AuthInterceptorModule} from 'app/services/auth-interceptor/auth-interceptor';
import {OrganisationIdInterceptorModule} from 'app/services/organisation-id-interceptor/organisation-id-interceptor';

// Avoid
import {API_URL} from '../../constants/api-url.constant';
import {AuthInterceptorModule} from '../services/auth-interceptor/auth-interceptor';
import {OrganisationIdInterceptorModule} from '../services/organisation-id-interceptor/organisation-id-interceptor';

Templates

Use the one-time binding syntax when data does not change after first render.

Why: Avoids unnecessary expensive $watchers.

<!-- Recommended -->
<p>Name: {{::ctrl.name}}</p>

<!-- Avoid -->
<p>Name: {{ctrl.name}}</p>

Anti-Patterns

• Don’t use ngInit – use controllers instead.
• Don’t use <div ng-controller="Controller"> syntax. Use directives instead.

General Patterns and Anti-Patterns

Rules that pertain to our application at large, not a specific part of Angular.

Patterns

Angular abstractions

Use:

• $timeout instead of setTimeout
• $interval instead of setInterval
• $window instead of window
• $document instead of document
• $http instead of $.ajax
• $q (promises) instead of callbacks

Why: This makes tests easier to follow and faster to run as they can be executed synchronously.

Dependency injection annotations

Always use array annotation for dependency injection and bootstrap with strictDi.

Why: Negates the need for additional tooling to guard against minification and strictDi throws an error if the array (or $inject) syntax is not used.

// Recommended
angular.module('CreditorsShowControllerModule', [])
  .controller('CreditorsShowController', [
    'creditor', 'payments', 'payouts',
    function CreditorsShowController(creditor, payments, payouts) {
      var ctrl = this;

      _.extend(ctrl, {
        creditor: creditor,
        payments: payments,
        payouts: payouts
      });
    }
  ]);

// Avoid
angular.module('CreditorsShowControllerModule', [])
  .controller('CreditorsShowController',
    function CreditorsShowController(creditor, payments, payouts) {
      var ctrl = this;

      _.extend(ctrl, {
        creditor: creditor,
        payments: payments,
        payouts: payouts
      });
    });

// Recommended
import {MainModule} from './main';

angular.element(document).ready(function() {
  angular.bootstrap(document.querySelector('[data-main-app]'), [
    MainModule.name
  ], {
    strictDi: true
  });
});

// Avoid
import {MainModule} from './main';

angular.element(document).ready(function() {
  angular.bootstrap(document.querySelector('[data-main-app]'), [
    MainModule.name
  ]);
});

Anti-patterns

Don’t use the $ name space in property names (e.g. $scope.$isActive = true).

Why: Makes clear what is an Angular internal.

Don't use globals. Resolve all dependencies using Dependency Injection.

Why: Using DI makes testing and refactoring easier.

Don't do if (!$scope.$$phase) $scope.$apply(), it means your $scope.$apply() isn't high enough in the call stack.

Why: You should $scope.$apply() as close to the asynchronous event binding as possible.

Credits

We referred to lots of resources during the creation of this styleguide, including:

• Todd Motto's styleguide
• John Papa's styleguide
• Minko Gechev's styleguide
• Google AngularJS and Closure styleguide
• The Angular.js GitHub wiki
• Digging into Angular's "Controller as" syntax, by Todd Motto
• Python PEP 8 Styleguide