jquery Deferred

三个异步任务， 顺序执行

var step1 = function(){
    var def = $.Deferred();
    setTimeout(function(){
        console.log('我是第一个任务');
        def.resolve();
    },3000)

    return def.promise();
}

var step2 = function(){
    var def = $.Deferred();
    setTimeout(function(){
        console.log('我是第二个任务');
        def.resolve();
    },5000)

    return def.promise();
}



var step3 = function(){
    var def = $.Deferred();
    setTimeout(function(){
        console.log('我是第三个任务');
        def.resolve();
    },1000)

    return def.promise();
}

step1().then(step2).then(step3)

三个任务 最后一个等待第一个 第二个完成后才触发

// 异步执行

var step1 = function(){
	var def = $.Deferred();
	setTimeout(function(){
		console.log('我是第一个任务');
		def.resolve();
	},3000)

	return def.promise();
}

var step2 = function(){
	var def = $.Deferred();
	setTimeout(function(){
		console.log('我是第二个任务');
		def.resolve();
	},1000)

	return def.promise();
}



var step3 = function(){
	var def = $.Deferred();
	setTimeout(function(){
		console.log('我是第三个任务');
		def.resolve();
	},300)

	return def.promise();
}

$.when(step1(), step2()).then(step3);