html5 canvas 绘制base64图片失败

Question

<canvas id="canvas1" ...> <!--源//-->
<canvas id="canvas2" ...> <!--目的//-->
<img id="testImg" src=""> <!--测试//-->

场景：
2个canvas;1个img

canvas1显示内容，接着将内容复制到canvas2里面。

实现：

var img = canvas1Context.toDataURL('image/jpeg');
img.replace(/^data:image\/(png|jpg);base64,/, "");
myTestImg.src = img;//显示成功！

var imggg = new Image();
imggg.src = img;
//img.length    //7259
canvas2Context.drawImage(imggg, 0, 0, 320, 480);
//黑底，无图像，无报错
//png格式是白底，同样无图像

Answer 1

 var imggg = new Image();
imggg.onload=function(){///////////放onload中试试
canvas2Context.drawImage(imggg, 0, 0, 320, 480);
}
imggg.src = img;