How to send HTTP GET requests from Angular to a backend API

How to send HTTP GET requests from Angular to a backend API
Below is a quick set of examples to show how to send HTTP GET requests from Angular to a backend API.
Originally published at https://jasonwatmore.com

Simple GET request with response type <any>

This sends an HTTP GET request to the npm api for a list of packages that belong to the @angular scope, then assigns the total returned in the response to the local property totalAngularPackages. The response type is set to <any> so it handle any properties returned in the response.

this.http.get<any>('https://api.npms.io/v2/search?q=scope:angular').subscribe(data => {
   this.totalAngularPackages = data.total;
})

GET request with strongly typed response

This sends the same request as the above but sets the response type to a custom SearchResults interface that defines the expected response properties.

interface SearchResults {
   total: number;
   results: Array<object>;
}
 
this.http.get<SearchResults>('https://api.npms.io/v2/search?q=scope:angular').subscribe(data
=> {
   this.totalAngularPackages = data.total;
})

GET request with error handling

This sends a request to an invalid url on the npm api and logs the error to the console from an error handler function that is passed as the second parameter to the subscribe() method of the Observable returned from the call to http.get().

this.http.get('https://api.npms.io/v2/invalid-url').subscribe(
   data => this.totalAngularPackages = data.total,
   error => console.error('There was an error!', error)
)

Prerequisites for making HTTP request from Angular

Before making HTTP requests from your Angular app you need to do a couple of things.

1. Add the HttpClientModule to the imports array of your AppModule like below on lines 3 and 10.

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { HttpClientModule } from '@angular/common/http';

import { AppComponent } from ‘./app.component’;

@NgModule({
   imports: [
       BrowserModule,
       HttpClientModule
   ],
   declarations: [
       AppComponent
   ],
   bootstrap: [AppComponent]
})
export class AppModule { }

2. Import the HttpClient into your component and add it to the constructor() params like below on lines 2 and 8.

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

@Component({ selector: ‘app’, templateUrl: ‘app.component.html’ })
export class AppComponent implements OnInit {
   totalAngularPackages;

   constructor(private http: HttpClient) { }

   ngOnInit() {     
        // Simple GET request with response type <any>
       this.http.get<any>(‘https://api.npms.io/v2/search?q=scope:angular’).subscribe(data => {
           this.totalAngularPackages = data.total;
       })
   }
}

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