代码应该没有出问题吧。。。

var aneObj=function()
{
 this.x=[];
 this.len=[];
}
aneObj.prototype.num=50;
aneObj.prototype.init=function()
{
 for(var i=0;i<this.num;i++)
 {
  this.x[i]=i*16+Math.random()*20;//[0,1)
        this.len[i]=200+Math.random()*50;
 }
}
aneObj.prototype.draw=function()
{
 ctx2.save();
 ctx2.globalAlpha=0.6;
 ctx2.lineWidth = 20;
 ctx2.lineCap = "round";
 ctx2.strockeStyle = "#de47ac";
 for(var i=0;i<this.num;i++)
 {
  //beginPath,moveTo,LineTo,strokeStyle,linWidth,LineCap,globalAlpha
  ctx2.beginPath();
  ctx2.moveTo(this.x[i],canHeight);
  ctx2.lineTo(this.x[i],canHeight - this.len[i]);
  ctx2.stroke();
 }
 ctx2.restore();
}