Object.watch.js

// inspired by jQuery watch: http://plugins.jquery.com/files/jquery-watch.js.txt

(function(){
	
	var watch = Object.prototype.watch,
		unwatch = Object.prototype.unwatch,
		watched = [],
		timer;
	
	Object.watch = function(obj, prop, fn){
		if (watch) return watch.call(obj, prop, fn);
		
		Object.unwatch(obj, prop);	// one at a time pls
		
		watched.push({
			obj: obj,
			prop: prop,
			last: obj[prop],
			fn: fn
		});
		
		if (!timer) timer = setInterval(function(){
			for (var w, i = watched.length; w = watched[--i]; ){
				if (w.obj[w.prop] !== w.last)
					w.obj.last = w.obj[w.prop] = w.fn.call(w.obj, w.prop, w.last, w.obj[w.prop]);
			}
		}, 100);
	};
	
	Object.unwatch = function(obj, prop){
		if (unwatch) return unwatch.call(obj, prop);
		
		for (var w, i = watched.length; w = watched[--i]; ){
			if (w.obj == obj && w.prop == prop){
				watched.splice(i, 1);
				break;
			}
		}
		
		if (!watched.length) timer = clearInterval(timer);
	};
	
})();