果实出不来

var fruitObj = function(){

this.alive = [];

this.x = [];

this.y = [];

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] = true;

this.x[i] = 0;

this.y[i] = 0;

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++) {

ctx2.drawImage(this.orange, this.x[i]-this.orange.width*0.5, this.y[i]-this.orange.height*0.5);

}

}

fruitObj.prototype.born = function(){

var aneID = Math.floor(Math.random() * ane.num);

this.x = ane.x[aneID];

this.y = canHeight - ane.len[aneID];

}

fruitObj.prototype.update = function(){

var num = 0;

for (var i = 0; i < this.num; i++) {

if (this.alive[i]) num++;

}

}

当我把this.born(i）注释掉的时候。黄色小球会在左上角出现。不注释的时候就没有小球出现