typescript - AngularJS - Use ES6 imports instead of angular DI system

Question

I'm using Webpack with angular 1.6.x and Typescript and I quit using angular DI in favor of ES6 imports. When I need some ng functions like $http, $resource and such I inject them directly using the angular.injector function through a decorator, like this:

// inject.ts
    import * as angular from 'angular';

    export function inject (...params: string[]) {

        function doCall ( param: string, klass: Function) {
            const injector = angular.injector([ 'ng' ]);
            const service = injector.get(param);
            try {
                klass.prototype[ param ] = service;
            } catch ( e ) {
                window.console.warn( e );
            }
        }

        // tslint:disable-next-line:ban-types
        return function ( klass: Function ) {
            params.forEach( ( param ) => {
                doCall( param, klass );
            } );
        };
    }

// posts.service.ts
import { inject } from './inject';
import { IPost, Post } from './post';

@inject('$http')
export class PostsService {
    public $http: angular.IHttpService;
    get (): Promise<IPost[]> {
        const posts: IPost[] = [];
        const promise = new Promise<IPost[]>( (resolve, reject) => {
            this.$http.get<IPost[]>('https://jsonplaceholder.typicode.com/posts')
            .then(( response ) => {
                response.data.forEach(item => {
                    posts.push( new Post(item) );
                });

                resolve( posts );
            });
        });

        return promise;
    }
}


// post.ts
export interface IPost {
    userId: number;
    id: number;
    title: string;
    body: string;
}
export class Post implements IPost {
    userId: number;
    id: number;
    title: string;
    body: string;

    constructor (item: IPost) {
        this.userId = item.userId;
        this.id = item.id;
        this.title = item.title;
        this.body = item.body;
    }
}


// controller.ts
import { IPost } from './post';
import { PostsService } from './posts.service';

export class Controller {
    public postService: PostsService;
    public posts: IPost[];
    constructor ( private $scope: angular.IScope ) {
        this.postService = new PostsService();
    }

    $onInit () {
        this.postService.get()
        .then((posts) => {
            this.posts = posts;
            this.$scope.$digest();
        });
    }
}

// index.ts
import * as angular from 'angular';

import { Controller } from './app/controller';

import './index.scss';

export const app: string = 'app';

angular
  .module(app, [])
  .controller('controller', Controller);


angular.bootstrap(document.body, [app]);

I don't know if it's in compliance with best practices or not, but it is working quite nicely so far.

I would like to hear your thoughts on the subject: is there any problem (performance, bad practice and such) using this approach?

Answer 1

ES modules cannot replace Angular modules and DI. They compliment each other and keep the application modular and testable.

ES6 modules provide extra layer of extensibility, for example controller/service subclassing (something that doesn't look good with Angular modules and DI alone).

The recommended approach with ES6 or TypeScript is to do DI conventionally, with $inject annotation:

export class PostsService {
  static $inject = ['$http'];
  constructor(
    public $http: angular.IHttpService
  ) {}
  ...
}

It's also a good practice to have one module per file, this way the application stays modular and testable:

export default angular.module('app.posts', [])
  .service('posts', `PostsService)
  .name;`

Its default export is module name that can be imported in another module that directly depends on it:

import postsModule from '...';
...
export default angular.module('app.controller', [postsModule])
  .controller('controller', Controller)
  .name;`

Application injector cannot be normally reached from a decorator. Even if it's possible with a hack to make it work in production, it will be messed up in tests.

angular.injector creates new injector (i.e. application instance) and has very limited proper uses in production:

angular.injector(['ng']).get('$rootScope') !== angular.injector(['ng']).get('$rootScope');

It is often misused when a developer doesn't know how to get current $injector instance. It certainly shouldn't be used in a case like this one.