What I wish JS could do.

gistfile1.js

function render() {
  var pixels = get_pixels();
  new Thread(function () {
    for (i = 0, len = pixels.length; i < len; i +=4) {
      // holy shared process memory batman!
      // manipulate pixels here
    }

    finished();
  });
}

function finished() {
  // done!
}