var fruitobj=function()
{
    this.alive =[];//bool
    this.x =[];
    this.y =[];
    this.l =[];
    this.spd =[];
    this.orange = new Image();
    this.blue = new Image();
}
fruitobj.prototype.num = 30;
fruitobj.prototype.init = function()
{
    for(var i =0; i< this.num; i++)
    {
        this.alive[i] = false;
        this.x[i] = 0;
        this.y[i] = 0;
        this.spd[i] = Math.random() * 0.01 + 0.005;//[0.005,0.015)
        this.born(i);
    }
    this.orange.src = "./src/fruit.png";
    this.blue.src = "./src/blue.png";
}
fruitobj.prototype.draw =function()
{
    for(var i =0; i< this.num; i++)
    {
        //draw
        //find an ane,grow,flyup
        if(this.alive[i])
        {
                     if(this.l[i] <= 14)
            {
                     this.l[i] += this.spd[i] * deltaTime;
            }
            else
            {
                     this.y[i] -= this.spd[i] * 7 * deltaTime;
            }
            ctx2.drawImage(this.orange,this.x[i] - this.l[i] * 0.5,this.y[i] -  this.l[i] * 0.5,this.l[i],this.l[i]);
            if(this.y[i] < 10)
            {
                     this.alive[i]=false;
            }
        }
    }
}
fruitobj.prototype.born = function(i)
{
    var aneID = Math.floor(Math.random() * ane.num);
    this.x[i] = ane.x[aneID];
    this.y[i] = canHeight - ane.len[aneID];
    this.l[i] = 0;
    this.alive[i] = true;
}
function fruitMonitor()
{
    var num =0;
    for(var i = 0; i < fruit.num; i++)
    {
        if(fruit.alive[i]) num++;
    }
    if(num < 15)
    {
        //send fruit
        sendFruit();
        return;
    }
}
function sendFruit()
{
    for(var i = 0; i < fruit.num; i++)
    {
        if(!fruit.alive[i])
        {
            fruit.born(i);
            return;
        }
    }
}

不循环呀  大神求指点