//同步流程

var series=function(arr){

    function async(i){

        arr[i](function(){

            if(1+i<arr.length){

                async(1+i)

            }

        })

    }

    async(0)

}

//demo

var back1=function(callback){

    setTimeout(function(){

        cc.log(21)

        callback()

    },1000)

}

series([back1,back1,back1])