[FR] APP_BASE_HREF useFactory Promise Support

[maks-humeniuk]

I'm submitting a...

[x] Feature request

Current behavior

APP_BASE_HREF useFactory doesn't support promises, only values.

Expected behavior

APP_BASE_HREF useFactory supports both values and promises.

What is the motivation / use case for changing the behavior?

In my application I need to set APP_BASE_HREF asynchronously. Unfortunately, APP_BASE_HREF useFactory doesn't support promises. So, I tried this approach with APP_INITIALIZER, but failed as well as OP, because it seems like if you do AJAX requests in APP_INITIALIZER useFactory, you should setup APP_BASE_HREF first.

APP_INITIALIZER supports promises in useFactory, so it would be very useful if APP_BASE_HREF supports them too.

Environment

Angular version: 6.0.0

Browser:
- [x] Chrome (desktop) version 69

[mlc-mlapis]

@Halfist ... ConfigService as the dependency has to specify the value and this is available for the factory function which returns the final value.
export function getBaseHref(configService: ConfigService): string {return configService.myBaseHref;}
{ provide: APP_BASE_HREF, useFactory: getBaseHref, deps: [ConfigService] }

[maks-humeniuk]

@mlc-mlapis, this is pretty much the same. configService.myBaseHref should be initialized first. In my case this initialization should occur asynchronously. Since APP_BASE_HREF useFactory doesn't support promises, I initialize it in APP_INITIALIZER useFactory. But APP_BASE_HREF useFactory executes before APP_INITIALIZER useFactory promise resolves. So, configService.myBaseHref is undefined.

[mlc-mlapis]

@Halfist ... how so when ConfigService is the dependency for both? ConfigService has to be instantiated first.

[mlc-mlapis]

@Halfist ... OK, I can see now. So you have to use some environment direct import or sync request.

[mlc-mlapis]

@Halfist ... just for curiosity ... what is printed when you inject location into the 'ConfigService`?

import { Location } from '@angular/common';
...
constructor(public location: Location) {
   console.log(location.prepareExternalUrl('/'));
}

[maks-humeniuk]

@mlc-mlapis, I just figured out that the requested feature won't help me at all. The irony is that I need to get base path from AJAX request in APP_BASE_HREF useFactory. But in order to make the request, base path should already be defined, otherwise the request URL prefix is undefined. If I'm right, the issue could be closed.

[mlc-mlapis]

@Halfist ... OK.

[maks-humeniuk]

Though, it could be helpful for other scenarios. Let it remain opened then.

[VitaliPark]

Here's another use case, when supporting promises in APP_BASE_HREF might be useful:
You need to set app base href dynamically using external configuration.

• In order to get this external configuration you can use APP_INITIALIZER (download config file via http call)
• But then, in useFactory of APP_BASE_HREF provider you need to wait for this call to finish to get config. And since you can only use value there, it's not possible (correct me if I'm wrong).
  Seems like currently the only way to do so, is to move config loading into main.ts file, and bootstrap application only after all configs are loaded and pass config in extra providers like so (again correct me if I'm wrong) :

fetchConfig().then(config => {
	platformBrowserDynamic([{provide: ConfigData, useValue: config}])
		.bootstrapModule(AppModule)
		.catch(err => console.log(err));
});

Which seems like a hack, especially when APP_INITIALIZER is used specifically for app initialization, but you can't use it in this particular case.

The same issue is described here: https://stackoverflow.com/questions/46190280/angular-2-set-app-base-href-with-a-value-from-a-promise-observable

[mightymatth]

Is there any progress about that? This strongly limits our use-case as we want to have base app href dynamically configurable. Thanks.

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