JavaScript：把img对象转化为base64

把img对象的src转化为base64

var canvas = document.createElement("canvas"); 
canvas.width = img.width; 
canvas.height = img.height; 
var ctx = canvas.getContext("2d"); 
ctx.drawImage(img, 0, 0, img.width, img.height); 
var dataURL = canvas.toDataURL("image/png"); 
console.log(dataURL);