Insanely Fast Javascript thread Yield (see blog post)

Soon (Fast)

// See http://www.bluejava.com/4NS/Speed-up-your-Websites-with-a-Faster-setTimeout-using-soon
// This is a very fast "asynchronous" flow control - i.e. it yields the thread and executes later,
// but not much later. It is far faster and lighter than using setTimeout(fn,0) for yielding threads.
// Its also faster than other setImmediate shims, as it uses Mutation Observer and "mainlines" successive
// calls internally.
// WARNING: This does not yield to the browser UI loop, so by using this repeatedly
// 		you can starve the UI and be unresponsive to the user.
// This is an even FASTER version of https://gist.github.com/bluejava/9b9542d1da2a164d0456 that gives up
// passing context and arguments, in exchange for a 25x speed increase. (Use anon function to pass context/args)
var soon = (function() {

		var fq = []; // function queue;

		function callQueue()
		{
			while(fq.length) // this approach allows new yields to pile on during the execution of these
			{
				fq[0]();  // no context or args..
				fq.shift(); // remove element just processed... do this after processing so we don't go 0 and trigger soon again
			}
		}

		// run the callQueue function asyncrhonously, as fast as possible
		var cqYield = (function() {

				// This is the fastest way browsers have to yield processing
				if(typeof MutationObserver !== "undefined")
				{
					// first, create a div not attached to DOM to "observe"
					var dd = document.createElement("div");
					var mo = new MutationObserver(callQueue);
					mo.observe(dd, { attributes: true });

					return function(fn) { dd.setAttribute("a",0); } // trigger callback to
				}

				// if No MutationObserver - this is the next best thing - handles Node and MSIE
				if(typeof setImmediate !== "undefined")
					return function() { setImmediate(callQueue) }

				// final fallback - shouldn't be used for much except very old browsers
				return function() { setTimeout(callQueue,0) }
			})();

		// this is the function that will be assigned to soon
		// it takes the function to call and examines all arguments
		return function(fn) {

				// push the function and any remaining arguments along with context
				fq.push(fn);

				if(fq.length == 1) // upon adding our first entry, kick off the callback
					cqYield();
			};

	})();