Guided: Working with Web Workers

Welcome to this Working with Web Workers lab, where you’ll build a number-crunching web app!

You’ll use Web Workers to perform heavy calculations, like generating Fibonacci sequences, in a background thread, ensuring the UI remains responsive. You’ll learn to create Web Workers, communicate with them using postMessage(), and manage their lifecycle.

The goal is to create a performant app that handles intensive tasks efficiently, equipping you with skills for real-world web development.

Web Workers are essential for modern web applications, allowing you to offload heavy tasks to background threads.

Without Web Workers, complex calculations can freeze the UI, frustrating users. In this app, a Web Worker will compute Fibonacci numbers while the main thread keeps the UI interactive, demonstrating the power of parallel processing in the browser.

Communication between threads and proper worker management are critical for reliable apps. You’ll use postMessage() and onmessage to exchange data and handle worker errors to ensure smooth operation.

These skills will help you build responsive, high-performance web applications, starting with this number-crunching app.

info> If you get stuck, you can reference the solutions folder containing the full code solution for this lab! You can also view the latest code in the Web Browser tab by clicking the Refresh button.

You’ll begin by setting up your project to use a Web Worker.

This step focuses on creating the main HTML file, JavaScript for the main thread, and adding a separate worker script. These tasks lay the foundation for your Web Worker–based application. Web Workers require a separate script file to define their logic. This separation keeps the main thread free to handle UI tasks. Creating an HTML file with a simple UI sets the stage for user interaction. The main thread is responsible for loading and controlling the Web Worker. Setting up a separate JavaScript file for the main thread helps organizes your logic clearly. The Web Worker script (worker.js) defines the background thread’s logic. A placeholder onmessage handler sets up the worker to receive messages, preparing it for computations.

Now you’ll create and initialize the Web Worker to perform calculations.

This step focuses on instantiating a Web Worker in the main thread and setting up the initial communication. Creating a Web Worker is the foundation for running tasks in the background. Instantiating a Web Worker connects the main thread to the worker script, enabling background computations. This is the first step in delegating tasks to a separate thread.

You create a Web Worker by using the Worker constructor and storing the instance in a variable. The main thread must process results from the Web Worker. In main.js, you can attach an onmessage event listener to the worker to handle the results and update the UI. Use this handler to log the data and display it in the app.

Next, you’ll implement messaging between the main thread and the Web Worker to perform Fibonacci calculations.

This step focuses on using postMessage() to send inputs and receive results, and defining the worker’s computation logic. Messaging is key to coordinating tasks across threads. Sending user input to the Web Worker via a button click enables the app to trigger computations. This connects the UI to the worker’s logic.

You can add a click event listener to the button to read the input value and send it to the worker using postMessage(). The Web Worker must perform the Fibonacci computation to offload work from the main thread. This implements the core functionality of the app.

You can update the onmessage handler in worker.js to compute the Fibonacci sequence and send the result back.

You’ll now enhance your app by managing the Web Worker’s lifecycle and adding error handling.

This step focuses on terminating the worker when needed and catching errors from the worker. Proper management ensures efficient resource use and a robust user experience. Terminating the Web Worker frees up resources and improves efficiency. A Stop button gives users control over the worker’s lifecycle.

You can add a Stop button to index.html, and in main.js, a click event listener that calls worker.terminate(). Validating inputs in the worker prevents errors during computation, improving reliability. Sending error messages informs the main thread of issues.

You can add input validation in worker.js’s onmessage handler and send error messages via postMessage(). Catching worker errors in the main thread ensures that users are informed of issues such as script errors and enhances the user experience.

To complete the app's error handling, add an onerror handler to the worker that displays the error message in the result div.

Great job—you’ve built a number-crunching app with Web Workers!

You’ve completed a practical project that demonstrates how to use Web Workers to perform heavy computations without freezing the UI. This lab has equipped you with valuable skills for building performant web applications.

You’ve learned how to create Web Workers to run tasks in the background, keeping the UI responsive. With messaging, you used postMessage() and onmessage to communicate between threads. Managing workers and handling errors ensured your app is efficient and user-friendly. These skills are essential for optimizing real-world web applications.

Now, consider use cases where Web Workers shine, such as processing large datasets (for example image filtering or data analysis) or running simulations. To enhance this app, try adding a progress indicator by sending intermediate results from the worker. You could also experiment with multiple workers for parallel tasks. For a challenge, try implementing a Web Worker to handle real-time data processing, like streaming JSON data.

I hope this lab inspires you to explore more JavaScript video courses and code labs to continue your learning journey here, at Pluralsight!