Understanding exhaustMap in Angular: A Simple Guide

In Angular, handling asynchronous operations is a common task, especially when working with HTTP requests, user input, or any event-driven programming. RxJS, a powerful library for reactive programming, provides several operators to manage these asynchronous operations efficiently. One such operator is exhaustMap. In this blog, we'll delve into what exhaustMap is, why and where to use it, and its benefits, along with a real-life example.

What is exhaustMap?

exhaustMap is an RxJS operator used to map each value from an observable to a new observable, then flatten all of these inner observables using an exhaust strategy. Essentially, it ignores all subsequent inner observables while the current inner observable is still executing. Once the current inner observable completes, it will consider new values and create a new inner observable.

Why Use exhaustMap?

1. Prevent Overlapping Requests:

When you have a situation where multiple asynchronous operations can be triggered in quick succession, you might want to prevent overlapping requests. exhaustMap ensures that only one inner observable is active at any given time. This is particularly useful in scenarios where starting a new operation before the previous one completes could lead to undesirable results, such as multiple API calls or form submissions.

2. Efficient Resource Utilization:

By ignoring new values while an inner observable is still executing, exhaustMap helps in efficiently utilizing resources. It ensures that only necessary operations are performed, reducing the load on your server or application.

Where to Use exhaustMap?

1. Form Submissions:

In forms where users can click a submit button multiple times, you want to prevent multiple submissions until the current one is processed. exhaustMap is perfect for this scenario.

2. Search or Filter Requests:

When implementing a search feature where each keystroke triggers an API call, using exhaustMap can prevent multiple overlapping API requests, improving performance and reducing server load.

3. User Interactions:

In any scenario where user interactions can trigger multiple events (like button clicks or keyboard events), exhaustMap helps manage these interactions efficiently.

Benefits of Using exhaustMap

• Prevents Multiple Executions: Ensures that only one inner observable is active at a time, preventing multiple executions.
• Efficient Resource Management: Reduces unnecessary operations, optimizing performance.
• Simplifies Code: Makes the code more readable and easier to maintain by managing complex asynchronous operations effectively.

Real-Life Example: Preventing Multiple Form Submissions

Let's consider a real-life example where exhaustMap can be beneficial. Imagine you have a login form in your Angular application. You want to prevent multiple submissions if the user clicks the submit button repeatedly.

Step-by-Step Implementation

1. HTML Template:

<form (ngSubmit)="onSubmit()" #loginForm="ngForm">
  <input type="text" name="username" ngModel required>
  <input type="password" name="password" ngModel required>
  <button type="submit">Login</button>
</form>        

2. Component:

import { Component } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { exhaustMap } from 'rxjs/operators';
import { fromEvent } from 'rxjs';

@Component({
  selector: 'app-login',
  templateUrl: './login.component.html'
})
export class LoginComponent {
  constructor(private http: HttpClient) {}

  onSubmit() {
    const loginButton = document.querySelector('button[type="submit"]');
    fromEvent(loginButton, 'click')
      .pipe(
        exhaustMap(() => this.login())
      )
      .subscribe(response => {
        console.log('Login successful:', response);
      }, error => {
        console.error('Login failed:', error);
      });
  }

  login() {
    const credentials = { username: 'user', password: 'password' };
    return this.http.post('/api/login', credentials);
  }
}
        

Explanation

• HTML Template: The form includes input fields for username and password, and a submit button.
• Component:We use fromEvent to create an observable from the button click event.exhaustMap is applied to the observable to manage the login requests.The login method returns an observable of the HTTP POST request.While an HTTP request is in progress, any additional button clicks will be ignored until the request completes.

Benefits in This Scenario

• Prevents Multiple Submissions: Ensures that only one login request is processed at a time.
• Efficient Resource Utilization: Reduces unnecessary server load by preventing multiple concurrent requests.
• Improved User Experience: Prevents potential errors or issues caused by multiple form submissions.

Conclusion

exhaustMap is a powerful RxJS operator that helps manage complex asynchronous operations in Angular applications. By ensuring that only one inner observable is active at a time, it prevents overlapping requests, optimizes resource utilization, and simplifies code management. Whether you're dealing with form submissions, search requests, or user interactions, exhaustMap can enhance the efficiency and performance of your application.