Web App Working Bar - Like GMail

promise_working_bar.js

var WorkerBar = (function(){
	var promises = [];
	var workingbar = $('.working');
	var done;

	var add = function(promise) {
		if ( promises.length == 0 ){
			showWorking();
		}

		// push new promise
		promises.push(promise);
		
		// re-register the when
		$.when.apply($, promises).done(function(){
			var doneCount = _.filter(promises, function(e){
				return e.state() === "resolved"
			}).length;
			
			if (doneCount === promises.length) {
				hideWorking();
			}
		});
	}

	var showWorking = function(){
		workingbar.show();
	}

	var hideWorking = function(){
		workingbar.hide();
		promises = [];
	}

	return {
		Add: add
	}
})();

var a = jQuery.Deferred();
var b = jQuery.Deferred();

setTimeout(function(){
	console.log('faking ajax request 1')
    WorkerBar.Add(a.promise());
},1000);

a.done(function(){
    console.log('request 1 is done')
});

b.done(function(){
    console.log('request 2 is done')
});

setTimeout(function(){
	console.log('faking ajax request 2')
    WorkerBar.Add(b.promise());
},2000);

setTimeout(function(){
    a.resolve()
},2000);

setTimeout(function(){
    b.resolve()
},4000);