ng-metadata is the answer to upgrading to Angular 2

06/16/20161 Min Read — In Angular

Earlier this week I spoke to making a poor man’s TypeScript Component decorator to begin to make Angular 1.x syntax more Angular 2.x compliant. Since then one of my coworkers brought to my attention a phenomenal library that extends on what I spoke to. ng-metadata is a library that allows you to wrap Angular 1.x code in TypeScript decorators to give the appearance of Angular 2 code. This is a huge benefit because it will allow for more gradual adoption of the Angular 2 specification.

This is a code snippet directly from ng-metadata that shows what your Angular 1.x Component code can be rewritten to look like

Angular 1.x with ngMetadata and Typescript:

// bootstrap.ts
import { bootstrap } from 'ng-metadata/platform';
import { HeroModule } from './hero';
// hero.ts
import * as angular from 'angular';
import { provide } from 'ng-metadata/core';
import { HeroComponent } from './hero.component';
import { HeroService } from './hero.service';
export const HeroModule = angular
.module('hero', [])
// hero.service.ts
import { Injectable, Inject } from 'ng-metadata/core';
export class HeroService {
constructor(@Inject('$http') private $http: ng.IHttpService) {}
fetchAll() {
return this.$http.get('/api/heroes');
// hero.component.ts
import { Component, Inject, Input, Output } from 'ng-metadata/core';
import { HeroService } from './hero.service';
selector: 'hero-cmp',
templateUrl: 'hero.html',
legacy: { transclude: true },
export class HeroComponent {
@Input() name: string;
@Output() onCall: Function;
// we need to inject via @Inject because angular 1 doesn't give us proper types
@Inject('$log') private $log: ng.ILogService,
// here we are injecting by Type
// which is possible thanks to reflect-metadata and Typescript and because our service
// is defined as a class
private heroSvc: HeroService
) {}
ngOnInit() {
/* your init logic */

I have to admit, this is a very impressive port. The only real criticism I have of this port is that it does not support Angular 2’s providers array in the Component decorator.

// app/app.component.ts
providers: [HeroService],
export class AppComponent implements OnInit {
title = 'Tour of Heroes';
heroes: Hero[];
selectedHero: Hero;
constructor(private heroService: HeroService) {}

That being said I think that what the team at ng-metadata has done with the Inject decorator is rather ingenious. I like that you can designate a service as @Injectable and forgo showing any code in your @Component or you can opt for the more explicit route and use @Inject in the constructor to make the DI function more obvious to the end developer.

For a more detailed breakdown of ng-metadata’s capabilities, please visit their API docs

UPDATE: 6/16/16

I was incorrect. ng-metadata does have support for the providers array out of the box!

ng-metadata — @Component

providers?Array<Injectables|string>Any providers that this component or any of it’s children depends on. This isn’t
doing anything for now, just for visual experience and mirroring ng2 api