Why Promises Don't Fix UI Freezes and How Web Workers Actually Do

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A technical deep-dive published on DEV Community explains a common misconception among JavaScript developers: using async/await or Promises does not move CPU-intensive work off the browser's main thread. When heavy computation runs on the main thread, the UI freezes regardless of async syntax, because Promises only manage waiting — not offloading work. Web Workers solve this by running code on a separate thread with its own call stack and event loop, keeping the UI responsive. The article walks through six hands-on examples, progressing from a frozen UI caused by a main-thread loop to advanced setups using Comlink, SharedArrayBuffer, and worker pools. All example projects are available on GitHub and cover both browser and Node.js environments.

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