waterfall实现

function TaskRun(tasks,done)
{
    var task_index=0;
    done=done||((err)=>{
        err&&console.log(err);
    });
    function next()    {
        if(task_index==tasks.length) {return done(null);}
        var args=[].slice.call(arguments);
        args.push(next);
        try{
            tasks[task_index++].apply(this,args);
        }catch(ex){
            return done(ex);
        }
    }
    next();　
}

TaskRun([function(next){
    setTimeout(function(){
        console.log("one");
         next(1);
     }, 10);
    
},function(num1,next){
    console.log("two");
    console.log(num1);
    throw new Error("sfdsf");
    setTimeout(function(){
        console.log("last");
         next(3,4);
     }, 10);
},function(num1,num2,next){
    console.log("5");
    console.log(num1);
    console.log(num2);
}])