Angular 9/8 How-To: Pass URL Query Parameters with HttpClient, HttpParams and fromString

  • Author: Ahmed Bouchefra

In this how-to article, we'll learn how to use fromString and HttpParams to pass query parameters to URLs or REST API endpoints.

Here, we assume we have a REST API endpoint named server.com/api/products with _page and _limit parameters.

We also assume, you have an Angular 9 project with the HttpClientModule imported in the main module or the module where you are implementing the requirement.

If you are new to these how-tos, check out how to install and set up a project and the prerequisites.

Step 1 - Generating and Implementing an Angular 9 Example Service

Head back to your terminal, navigate to your project's directory and run the following command to generate an Angular service:

$ ng generate service example

Next, open the src/app/example.service.ts file and update it as follows:

import { Injectable } from '@angular/core';
import { HttpClient, HttpErrorResponse } from "@angular/common/http";


@Injectable({
  providedIn: 'root'
})
export class ExampleService {

  constructor(private httpClient: HttpClient) { }
}

We import HttpClient and inject it via the service constructor.

Step 2 - Importing the Angular 9 HttpParams Interface

Next, import HttpParams in the src/app/example.service.ts file as follows:

import { HttpParams } from "@angular/common/http";

Step 3 - Sending a GET Request with Parameters

Next, define the sendGetRequestWithHttpParameters() method as follows:

  public sendGETRequestWithParameters(){
    const opts = { params: new HttpParams({fromString: "_page=1&_limit=10"}) };
    return this.httpClient.get("http://server.com/api/products", opts);
  }

We create an instance of HttpParams from the `page=1&limit=10string usingfromString. This way we pass the value of 1 to thepagequery parameter and 10 tolimit` query parameter.

You can also use the append() method of HttpParams to set and pass parameters:

  public sendGETRequestWithParameters(){    ```
    let params = new HttpParams();
    params = params.append('_page', 1);
    params = params.append('_limit', 10);

    return this.httpClient.get("http://server.com/api/products", {params: params});
   }

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