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Dzhavat Ushev for This is Angular

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Using Observable in APP_INITIALIZER

An exciting new feature is coming to Angular v12 - support for Observables in APP_INITIALIZER ๐ŸŽ‰

Note: This feature was added in v12.0.0-next.2.

Up until now, if you wanted to execute something asynchronous as part of APP_INITIALIZER, say an HTTP request to get some configuration, your only option was to convert it to a Promise. Often times using toPromise() (which, btw, is deprecated in the upcoming RxJS v7).

This is no more! In v12 you will be able to directly return an Observable. Letโ€™s see how:

import { APP_INITIALIZER, FactoryProvider } from '@angular/core';
import { ConfigService } from "./config.service";

function loadConfigFactory(configService: ConfigService) {
  // Easy as pie ๐Ÿฅง
  return () => configService.getConfig(); // ๐Ÿ‘ˆ

  // How you might've done it โ€œbeforeโ€
  // return () => configService.getConfig().toPromise();

export const loadConfigProvider: FactoryProvider = {
  useFactory: loadConfigFactory,
  deps: [ConfigService],
  multi: true
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An important thing to note is that the Observable must complete, otherwise the bootstrap process will not continue.

Now, place the loadConfigProvider variable in the providers array of a Module and everything should be working fine. Check out this Stackblitz to see it in action.

Oh, and donโ€™t forget to add error handling to that request. ๐Ÿ˜Ž

Thanks to Yadong Xie for this wonderful contribution.

Photo by Katerina Pavlyuchkova on Unsplash

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