Cross-browser and optimized way to postpone a function execution to next "tick".

later.js

// Based on the Q.nextTick implementation https://github.com/kriskowal/q/pull/195. 
var later = (function(){
	var head = { task: void 0, next: null }, tail = head,
		maxPendingTicks = 2, pendingTicks = 0, queuedTasks = 0, usedTicks = 0,
		requestTick;

	var onTick = function() {
		--pendingTicks;

		if ( ++usedTicks >= maxPendingTicks ) {
			// Amortize delay after thrown exceptions.
			maxPendingTicks *= 2;
			var expectedTicks = queuedTasks && Math.min( queuedTasks - 1, maxPendingTicks );
			while ( pendingTicks < expectedTicks ) {
				++pendingTicks;
				requestTick();
			}
			usedTicks = 0;
		}

		while ( queuedTasks ) {
			--queuedTasks; // decrement here to ensure it's never negative
			head = head.next;
			var task = head.task;
			head.task = void 0;
			task();
		}

		usedTicks = 0;
	};

	var later = function( task ) {
		tail = tail.next = { task: task, next: null };
		if ( ++queuedTasks > pendingTicks && pendingTicks < maxPendingTicks ) {
			++pendingTicks;
			requestTick();
		}
	};

	var win = typeof window !== "undefined" && window;

	if ( typeof process !== "undefined" && "nextTick" in process ) {
		requestTick = function() {
			process.nextTick( onTick );
		};

	} else if ( typeof win.setImmediate === "function" ) {
		requestTick = function() {
			win.setImmediate( onTick );
		};

	} else if ( typeof MessageChannel !== "undefined" ) {
		var channel = new MessageChannel();
		channel.port1.onmessage = onTick;
		requestTick = function() {
			channel.port2.postMessage(0);
		};

	} else {
		requestTick = function() {
			setTimeout( onTick, 0 );
		};

		if ( win && typeof Image !== "undefined" ) {
			var c = 0;

			var requestTickViaImage = function( cb ) {
				var img = new Image();
				img.onerror = cb || onTick;
				img.src = 'data:image/png,';
			};

			try {
				requestTickViaImage(function() {
					if ( --c === 0 ) {
						requestTick = requestTickViaImage;
					}
				});
				++c;
			} catch (e) {}

			c && setTimeout(function() {
				c = 0;
			}, 0);
		}
	}

	return later;
})();