Angular: Preventing Multiple HTTP Requests to the Same Endpoint in Different Components

Neil Menon · January 6, 2021

While working on my new project, lastfm-with-friends, I noticed that I was making a call to my backend user service multiple times in a single page load.

The Problem

I figured out it was because I need the data in several different components. My UserService had a function getUser() which simply returned the HttpClient’s Observable to the components:

getUser() {
    return this.http.get(config.api_root + '/users/' + this.user);

And in my components:

this.userService.getUser().toPromise().then(data => {
    this.user = data

So for every component I used this function, I got a separate call made to my backend. This is obviously a waste so I looked for a way to prevent multiple calls.

The Solution

After quite a bit of trial and error, I stumbled upon a solution that worked for me.

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { share } from 'rxjs/operators';
import { Observable } from 'rxjs';
import { config } from './config'

  providedIn: 'root'
export class UserService {
  username: string = localStorage.getItem("lastfm_username");
  user: Observable<any>;
  constructor(private http: HttpClient) { }
   * Prevent making multiple API requests for the same endpoint on different components.
   * Thanks to for solution
  getUser(): Observable<any> {
    if (this.user) {
      return this.user;
    } else {
      this.user = this.http.get(config.api_root + '/users/' + this.user).pipe(share());
      return this.user;

The basic idea here is to save the Observable from the first request in the UserService. When another components wants the data, the service will check if it already exists in the this.user variable. This seems pretty simple, but the real magic is in the share() function, which I learned allows a resource to be shared among multiple subscribers. Pretty convenient.

Now I am calling this getUser() function in several components and seeing only one backend call.

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