var wait = function(dtd) {
	var tasks = function() {
		alert("执行完毕！");
		dtd.resolve(); // 改变Deferred对象的执行状态　　　
	};
	setTimeout(tasks, 5000);
	return dtd.promise();　　
};

$.Deferred(wait)
.done(function() {
	alert("哈哈，成功了！");
}).fail(function() {
	alert("出错啦！");
});

from:http://www.ruanyifeng.com/blog/2011/08/a_detailed_explanation_of_jquery_deferred_object.html