HTML5 Rocks

HTML5 Rocks

Workers ♥ ArrayBuffer

By Eric Bidelman at

As of crbug.com/73313, Chrome 13 and FF5 support sending an ArrayBuffer (or Typed Array) to/from a Web Worker. For example:

worker.js

self.onmessage = function(e) {
  var uInt8Array = e.data;
  postMessage("Inside worker.js: uInt8Array.toString() = " + uInt8Array.toString());
  postMessage("Inside worker.js: uInt8Array.byteLength = " + uInt8Array.byteLength);
};

main.html

var uInt8Array = new Uint8Array(new ArrayBuffer(10));
for (var i = 0; i < uInt8Array.length; ++i) {
  uInt8Array[i] = i * 2; // [0, 2, 4, 6, 8,...]
}

console.log('uInt8Array.toString() = ' + uInt8Array.toString());
console.log('uInt8Array.byteLength = ' + uInt8Array.byteLength);

worker.postMessage(uInt8Array);

Why is this exciting?...binary data!

Instead of the browser serializing your postMessage() data to a JSON object, it uses the structured clone algorithm to copy the ArrayBuffer to the worker's context, and vice versa. This opens up a real potential for workers that we haven't seen before. That is, being able to easily pass binary data between main app and worker thread.

Typed array I/O makes intense image manipulation, sound processing, and heavy webgl calculations much more feasible. For example, one could read a File as an array buffer or fetch a Blob using XHR2 and pass the result directly to a worker. No more base64 encoding the data :)

In my opinion this is one of those nitpicks workers should have included from the start. It just makes sense.