Browser Support

Chrome 4+ · Firefox 3.5+ · Safari 4+ · Edge 12+ This practical example involves crypto.getRandomValues.

Overview

This section ties together everything you've learned: move Fibonacci calculation and large array sorting from main thread to Worker.

Scenario: You're building a data analysis page that needs to calculate Fibonacci #45 (takes ~3-5 seconds) and sort/aggregate 200,000 rows of CSV data simultaneously. If all this runs on main thread, page freezes for 5 seconds — user thinks it's broken.

We solve this with Dedicated Worker.

Effect Demo

After clicking "Run Computation":

Main thread immediately responds — button turns gray Disabled
Main thread not stuttering — can scroll, click other buttons

Worker silently computes in background for 5 seconds

After completion, main thread receives result, updates UI
"✓ Done, result: 1134903170, took 3ms"

Notes

• Transferable is key: Pass arr.buffer as second argument to postMessage — data is "transferred" not "cloned", main thread immediately releases that memory, no stuttering
• fibonacci uses matrix exponentiation not recursion: Recursive version O(2^n), matrix exponentiation O(log n), even #1000 computes instantly
• Worker has no DOM: Don't try to manipulate document inside Worker; all results must postMessage back to main thread
• Worker errors don't crash main thread: Worker errors can be caught with worker.onerror, main thread keeps running