application_init.ts
/**
* @license
* Copyright Google LLC All Rights Reserved.
*
* Use of this source code is governed by an MIT-style license that can be
* found in the LICENSE file at https://angular.io/license
*/
import {Observable} from 'rxjs';
import {Inject, Injectable, InjectionToken, Optional} from './di';
import {isObservable, isPromise} from './util/lang';
import {noop} from './util/noop';
/**
* A [DI token](guide/glossary#di-token "DI token definition") that you can use to provide
* one or more initialization functions.
*
* The provided functions are injected at application startup and executed during
* app initialization. If any of these functions returns a Promise or an Observable, initialization
* does not complete until the Promise is resolved or the Observable is completed.
*
* You can, for example, create a factory function that loads language data
* or an external configuration, and provide that function to the `APP_INITIALIZER` token.
* The function is executed during the application bootstrap process,
* and the needed data is available on startup.
*
* @see `ApplicationInitStatus`
*
* @usageNotes
*
* The following example illustrates how to configure a multi-provider using `APP_INITIALIZER` token
* and a function returning a promise.
*
* ```
* function initializeApp(): Promise<any> {
* return new Promise((resolve, reject) => {
* // Do some asynchronous stuff
* resolve();
* });
* }
*
* @NgModule({
* imports: [BrowserModule],
* declarations: [AppComponent],
* bootstrap: [AppComponent],
* providers: [{
* provide: APP_INITIALIZER,
* useFactory: () => initializeApp,
* multi: true
* }]
* })
* export class AppModule {}
* ```
*
* It's also possible to configure a multi-provider using `APP_INITIALIZER` token and a function
* returning an observable, see an example below. Note: the `HttpClient` in this example is used for
* demo purposes to illustrate how the factory function can work with other providers available
* through DI.
*
* ```
* function initializeAppFactory(httpClient: HttpClient): () => Observable<any> {
* return () => httpClient.get("https://someUrl.com/api/user")
* .pipe(
* tap(user => { ... })
* );
* }
*
* @NgModule({
* imports: [BrowserModule, HttpClientModule],
* declarations: [AppComponent],
* bootstrap: [AppComponent],
* providers: [{
* provide: APP_INITIALIZER,
* useFactory: initializeAppFactory,
* deps: [HttpClient],
* multi: true
* }]
* })
* export class AppModule {}
* ```
*
* @publicApi
*/
export const APP_INITIALIZER =
new InjectionToken<ReadonlyArray<() => Observable<unknown>| Promise<unknown>| void>>(
'Application Initializer');
/**
* A class that reflects the state of running {@link APP_INITIALIZER} functions.
*
* @publicApi
*/
@Injectable()
export class ApplicationInitStatus {
private resolve = noop;
private reject = noop;
private initialized = false;
public readonly donePromise: Promise<any>;
public readonly done = false;
constructor(@Inject(APP_INITIALIZER) @Optional() private readonly appInits:
ReadonlyArray<() => Observable<unknown>| Promise<unknown>| void>) {
this.donePromise = new Promise((res, rej) => {
this.resolve = res;
this.reject = rej;
});
}
/** @internal */
runInitializers() {
if (this.initialized) {
return;
}
const asyncInitPromises: Promise<any>[] = [];
const complete = () => {
(this as {done: boolean}).done = true;
this.resolve();
};
if (this.appInits) {
for (let i = 0; i < this.appInits.length; i++) {
const initResult = this.appInits[i]();
if (isPromise(initResult)) {
asyncInitPromises.push(initResult);
} else if (isObservable(initResult)) {
const observableAsPromise = new Promise<void>((resolve, reject) => {
initResult.subscribe({complete: resolve, error: reject});
});
asyncInitPromises.push(observableAsPromise);
}
}
}
Promise.all(asyncInitPromises)
.then(() => {
complete();
})
.catch(e => {
this.reject(e);
});
if (asyncInitPromises.length === 0) {
complete();
}
this.initialized = true;
}
}