17. HttpClient

Install HttpClientModule in AppModule:

import { HttpClientModule } from '@angular/common/http';

  imports: [
    BrowserModule,
    BrowserAnimationsModule,
    ReactiveFormsModule,
    FormsModule,
    HttpModule,
    HttpClientModule,
    DashboardModule,
    ArchitectureModule,
    AppRoutingModule,
    SharedModule,
    TechnologiesModule,
    LoginRoutingModule,
    QuestionsModule
  ]

get() method on HttpClient:

import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-http-client',
  template: `
        <h2>My Technologies</h2>
        <ul class="list-group">
            <li class="list-group-item list-group-item-primary" *ngFor="let result of results">
            {{ result }}
            </li>
        </ul>
  `
})
export class HttpClientComponent implements OnInit {

  private technologiesURL = 'api/results';
  results: string[];

  constructor(private httpClient: HttpClient) { }

  ngOnInit(): void {
    //make http request
    this.httpClient.get(this.technologiesURL).subscribe(data => {
      this.results = data as string[];
    });
  }

}

Let's view the results in our Chromium Web Browser:

Typechecking the response:

interface ResultsResponse {
  results: string[];
}


export class HttpClientComponent implements OnInit {

  private technologiesURL = 'api/results';
  results: ResultsResponse;

  constructor(private httpClient: HttpClient) { }

  ngOnInit(): void {
    this.httpClient.get<ResultsResponse>(this.technologiesURL).subscribe(data => {
      this.results = data;
    });
  }

}

Reading the full response:

  ngOnInit(): void {
    this.httpClient.get<any>(this.technologiesURL, { observe: 'response' }).subscribe(resp => {
      console.log(resp.headers.get('X-Custom-Header'));
      console.log(resp.body);
    });
  }

Error Handling:

import { Component, OnInit } from '@angular/core';
import { HttpClient, HttpErrorResponse } from '@angular/common/http';

import { Technology } from './technology';

import 'rxjs/add/operator/retry';

@Component({
  selector: 'app-httpclient',
  template: `
          <h2>My Technologies</h2>
          <ul>
              <li *ngFor="let technology of technologies">{{ technology.name }}</li>
          </ul>
  `
})
export class HttpClientComponent implements OnInit {
  private technologiesURL = 'api/technologies';
  technologies: Technology[] = [];

  constructor(private http: HttpClient) { }

  ngOnInit() {
      this.http.get<Technology[]>(this.technologiesURL)
               .retry(3)
               .subscribe(
                 results => { this.technologies = results; },
                 (err: HttpErrorResponse) => {
                      if (err.error instanceof Error) {
                      console.log('there was an error:', err.error.message);
                    } else {
                      console.log(`Backend returned code ${err.status}, body was: ${err.error}`);
                    }
               });
             }

}

Requesting NON-JSON data:

    getTextFile(): void {
      this.http.get('/motivation.txt', { responseType: 'text'})
               .subscribe(data => console.log(data));
    }

POST:

  add(name: string): void {
      name = name.trim();
      if (!name) { return; }
      const body = { id: counter++, name: name };
      this.technologies.push(body);
      this.http.post(this.technologiesURL, body).subscribe();
    }

Headers:

    add(name: string): void {
      name = name.trim();
      if (!name) { return; }
      const body = { id: counter++, name: name };
      this.technologies.push(body);
      this.http.post(this.technologiesURL, body, {
        headers: new HttpHeaders().set('Authorization', 'my-auth-token')
      }).subscribe();
    }

URL Parameters:

import { Component, OnInit } from '@angular/core';
import { HttpClient, HttpErrorResponse, HttpHeaders, HttpParams } from '@angular/common/http';

import { Technology } from './technology';

import 'rxjs/add/operator/retry';

let counter = 100;

@Component({
  selector: 'app-httpclient',
  template: `
          <h2>My Technologies</h2>
          New Technology: <input #box>
          <button (click)="add(box.value); box.value = '';">Add</button>
          <ul>
              <li *ngFor="let technology of technologies">{{ technology.name }}</li>
          </ul>
  `
})
export class HttpClientComponent implements OnInit {
  private technologiesURL = 'api/technologies';
  technologies: Technology[] = [];

  constructor(private http: HttpClient) { }

  ngOnInit() {
      this.http.get<Technology[]>(this.technologiesURL)
               .retry(3)
               .subscribe(
                 results => { this.technologies = results; },
                 (err: HttpErrorResponse) => {
                      if (err.error instanceof Error) {
                      console.log('there was an error:', err.error.message);
                    } else {
                      console.log(`Backend returned code ${err.status}, body was: ${err.error}`);
                    }
               });
      }

    add(name: string): void {
      name = name.trim();
      if (!name) { return; }
      const body = { name: name };
      this.http.post(this.technologiesURL, body, {
        params: new HttpParams().set('id', counter++ + '1')
      }).subscribe(technologies => this.technologies.push(technologies as Technology));
    }


    getTextFile(): void {
      this.http.get('/motivation.txt', { responseType: 'text'})
               .subscribe(data => console.log(data));
    }

}

Interceptor:

import { Injectable } from '@angular/core';
import { HttpEvent, HttpInterceptor, HttpHandler, HttpRequest } from '@angular/common/http';

import { Observable } from 'rxjs/Observable';

@Injectable()
export class NoopInterceptor implements HttpInterceptor {

        intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
          return next.handle(request);
        }

}

Provide for Interceptor:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';
import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';

import { AppRoutingModule } from './app-routing.module';

import { InMemoryWebApiModule } from 'angular-in-memory-web-api';
import { InMemoryDataService } from './in-memory-data.service';

import { AppComponent } from './app.component';
import { TechnologiesComponent } from './technologies.component';
import { TechnologyDetailComponent } from './technology-detail.component';
import { DashboardComponent } from './dashboard.component';
import { TechnologySearchComponent } from './technology-search.component';
import { HttpClientComponent } from './httpclient.component';

import { TechnologyService } from './technology.service';
import { TechnologySearchService } from './technology-search.service';
import { NoopInterceptor } from './noop-interceptor.service';

@NgModule({
  declarations: [
    AppComponent,
    TechnologiesComponent,
    TechnologyDetailComponent,
    DashboardComponent,
    TechnologySearchComponent,
    HttpClientComponent
  ],
  imports: [
    BrowserModule,
    FormsModule,
    HttpModule,
    HttpClientModule,
    InMemoryWebApiModule.forRoot(InMemoryDataService),
    AppRoutingModule
  ],
  providers: [{
      provide: HTTP_INTERCEPTORS,
      useClass: NoopInterceptor,
      multi: true
  },
  TechnologyService,
  TechnologySearchService
],
  bootstrap: [ AppComponent ]
})
export class AppModule { }

Mutate Request:

import { Injectable } from '@angular/core';
import { HttpEvent, HttpInterceptor, HttpHandler, HttpRequest } from '@angular/common/http';

import { Observable } from 'rxjs/Observable';

@Injectable()
export class NoopInterceptor implements HttpInterceptor {

        intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
          const duplicateRequest = request.clone();

          const secureRequest = request.clone({url: request.url.replace('http://', 'https://')});

          return next.handle(secureRequest);
        }

}

Setting New Headers: