Multithreading in React: A Guide to Web Workers

About this talk

JavaScript is single-threaded — but your CPU is not. This talk at the 10th edition of ReactJS Day in Verona explored the Web Workers API as a practical tool for moving heavy computation off the main thread, keeping React UIs responsive under load. From the basics of thread communication through `postMessage` to measuring real impact on frame rate and interaction latency, attendees left with a clear decision framework for when Web Workers are worth the complexity.

Key takeaways

• Why the single-threaded model breaks down under CPU-intensive workloads in React apps
• How Web Workers communicate with the main thread via structured cloning and Transferable objects
• Practical patterns: offloading data parsing, encryption, and heavy transformations
• Measuring the real impact on responsiveness using DevTools performance profiles