绘制静态果实的时候可以显示，但是添加上this.l[] 之后 在draw中打印this.l[i]时显示NaN

var fruitObj = function(){

this.alive = [];

this.x = [];

this.y = [];

this.l = [];

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++) {

//draw find an ane ,grow,fly up

console.log(this.l[i]);

this.l[i] += 0.01 * 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] );

}

}

//随机找一个海葵，果实长在海葵上

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;

}