What are Web Workers and how do they enable parallel processing in the browser?

Question

At a data visualization company: "Our chart rendering blocks the main thread for 2 seconds on 100K data points. Users can't interact during that time."

Interview OS Community · Accepted Answer

## Web Workers run in separate threads

```javascript
// main.js
const worker = new Worker("chart-worker.js");
worker.postMessage({ type: "render", data: largeDataset });
worker.onmessage = (e) => { document.getElementById("chart").innerHTML = e.data.chartSVG; };

// chart-worker.js — doesn't block UI!
self.onmessage = (e) => {
  const result = heavyChartComputation(e.data.data);
  self.postMessage({ chartSVG: result });
};
```

| Can Access | Cannot Access |
|-----------|---------------|
| fetch(), WebSocket | DOM (document, window) |
| IndexedDB | localStorage |
| importScripts() | UI elements |

Main thread stays interactive while worker processes data. Small overhead (~50ms to start worker).

Interview OS

What are Web Workers and how do they enable parallel processing in the browser?

Question Details

Suggested Solution

Web Workers run in separate threads

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