A Step-by-Step Guide to Using RxJS combineLatestWith

A Step-by-Step Guide to Using RxJS combineLatestWith

RxJS is a powerful library for handling asynchronous operations in JavaScript applications. One of its operators, combineLatestWith, enables you to combine the latest values from multiple observables into a single observable. In this step-by-step guide, we'll explore how to use combineLatestWith effectively in your RxJS code.

Prerequisites: Before you begin, make sure you have the following prerequisites:

  • Basic knowledge of JavaScript and RxJS.
  • Node.js installed on your system.
  • A code editor (e.g., Visual Studio Code).

Step 1: Set Up Your Environment

Start by creating a new JavaScript or TypeScript project and setting up the necessary dependencies. You can use npm or yarn to manage your project.

# Create a new project folder
mkdir combineLatestExample
cd combineLatestExample

# Initialize your project (choose one)
npm init -y
# OR
yarn init -y

# Install RxJS
npm install rxjs
# OR
yarn add rxjs

Step 2: Create Your First Observables

In this example, let's imagine you have two observables, observable1 and observable2, which emit values over time. We'll create simple observables for demonstration purposes:

// Import RxJS
const { of, interval } = require('rxjs');
const { combineLatestWith } = require('rxjs/operators');

// Create observables
const observable1 = of('A', 'B', 'C');
const observable2 = interval(1000); // Emits values every second

Step 3: Use combineLatestWith Operator

Now, let's combine the latest values from observable1 and observable2 using the combineLatestWith operator. This will create a new observable that emits an array containing the latest values from both observables whenever either of them emits a new value.

// Combine observables using combineLatestWith
const combinedObservable = observable1.pipe(

Step 4: Subscribe and Output the Results

To see the combined values in action, subscribe to the combinedObservable and log the results.

// Subscribe to the combined observable
combinedObservable.subscribe(([value1, value2]) => {
  console.log(`Latest values: ${value1} from observable1, ${value2} from observable2`);

Step 5: Run Your Code

Save your code in a file (e.g., main.js), and then run it using Node.js:

node main.js

You should see the combined values being logged to the console as they change over time.


In this step-by-step guide, you've learned how to use the RxJS combineLatestWith operator to combine the latest values from multiple observables. This operator is valuable for scenarios where you need to react to changes in multiple data sources simultaneously.

Feel free to adapt this example to your specific use cases and explore more advanced features of RxJS as you continue to build powerful and reactive applications.