[Angular] Tree shakable provider

When we create a Service, Angluar CLI will helps us to add:

@#Injectable({
  providedIn: ‘root‘
})

It only create a instance in root dependency tree. If there is no reference to use this provider, Angular will remove it from our production code.

But the service we created are Class based service, what if we want to create some Object and inject this Object to our application and we want to make it tre shakable as well.

We can do as following:

import { InjectionToken } from "@angular/core";
export interface AppConfig {
  apiUrl: string;
  courseCacheSize: number;
}

export const APP_CONFIG: AppConfig = {
  apiUrl: "http://localhost:9000",
  courseCacheSize: 10
};

// Use providedIn & factory to make it as tree shakable provider.
export const CONFIG_TOKEN = new InjectionToken<AppConfig>("CONFIG_TOKEN", {
  providedIn: "root",
  factory: () => APP_CONFIG
});

// Not tree shakable
// export const CONFIG_TOKEN = new InjectionToken<AppConfig>("CONFIG_TOKEN");

Whereever you use the provider, you need to remove it:

@Component({
  selector: "app-root",
  templateUrl: "./app.component.html",
  styleUrls: ["./app.component.css"],
  // Remove it when need to use tree shakable provider
  providers: [{ provide: CONFIG_TOKEN, useValue: APP_CONFIG }]
})

原文地址：https://www.cnblogs.com/Answer1215/p/10299461.html