Inject Http manually in Angular 4

Question

I want to manually bootstrap an Angular 4 app (created with CLI). In main.ts I am doing this:

const injector = ReflectiveInjector.resolveAndCrea         


        

Answer 1

You can use HttpClient service before the Angular starts using ReflectiveInjector like this:

import { ReflectiveInjector } from '@angular/core';
import { HttpClient, HttpClientModule } from '@angular/common/http';
const injector = ReflectiveInjector.resolveAndCreate(getAnnotations(HttpClientModule)[0].providers);

const http = injector.get(HttpClient);
http.get('/posts/1').subscribe((r) => {
  ConfigurationService.configuration = <Configuration>JSON.parse(config);
  platformBrowserDynamic().bootstrapModule(AppModule);
});

This line:

getAnnotations(HttpClientModule).providers

references all providers that are registered on the HttpClientModule so you don't have to specify them manually. This answer explains the getAnnotations function in great details.

The approach I've shown is "sort of" the similar to what you're doing when importing HttpClientModule into the AppModule:

@NgModule({
    imports: [HttpClientModule, ...],
})
export class AppModule {}

See this plunker for details.

Answer 2

Thanks, Kuncevic. I have come up with this solution, which works fine:

function httpGetAsync(theUrl, callback) {
  const xmlHttp = new XMLHttpRequest();

  xmlHttp.onreadystatechange = function() {
    if (xmlHttp.readyState === 4 && xmlHttp.status === 200) {
      callback(xmlHttp.responseText);
    }
  }

  xmlHttp.open('GET', theUrl, true); // true for asynchronous
  xmlHttp.send(null);
}

httpGetAsync('assets/configs/configuration.json', (config: string) => {
  ConfigurationService.configuration = <Configuration>JSON.parse(config);
  platformBrowserDynamic().bootstrapModule(AppModule);
});

Answer 3

As another approach you can use the native browser fetch api. So you do not have to deal with angular http, etc

That is how I am doing that:

fetch(configUrl, { method: 'get' })
.then((response) => {
  response.json()
    .then((data: any) => {
      if (environment.production) {
        enableProdMode();
      };
      platformBrowserDynamic([{ provide: AppSettings, useValue: new AppSettings(data.config) }]).bootstrapModule(AppModule);
    });
});

But bare in mind that fetch didn't get much love in old browsers so you need to polyfil that with whatwg-fetch like npm install whatwg-fetch --save then import 'whatwg-fetch' in polyfills.ts in order if you want to support old browsers.

UPDATE: Yeah you can use XMLHttpRequest but you are getting same browsers support with that as fetch just a modern replacement for XMLHttpRequest.

Answer 4

Possibly the original answer worked before, but in Angular 5 I was not able to use it, there was no definition for the function getAnnotations. This is what did work for me however:

import { ReflectiveInjector } from '@angular/core';
import {
  HttpClient,
  XhrFactory,
  HttpHandler,
  HttpXhrBackend,
  HttpBackend
} from '@angular/common/http';

// https://github.com/angular/angular/blob/master/packages/common/http/src/xhr.ts#L45
export class BrowserXhr implements XhrFactory {
  build(): any { return <any>(new XMLHttpRequest()); }
}

const injector = ReflectiveInjector.resolveAndCreate([
  HttpClient,
  HttpXhrBackend,
  { provide: HttpBackend, useExisting: HttpXhrBackend },
  { provide: HttpHandler, useExisting: HttpBackend },
  { provide: XhrFactory, useClass: BrowserXhr},
]);

const http: HttpClient = injector.get(HttpClient);

http.get('/url').subscribe((response) => {
  console.log(response);
});