图片转成base64

uploader.js

var img = new Image();
img.crossOrigin = "*";
img.src = "http://s3.steedos.com/users/5194c74a8e296a6cfe000019/admin/angel_galaxy-wallpaper-1440x900.jpg";

var canvas = document.createElement("canvas");
canvas.width = img.width;
canvas.height = img.width;
var ctx = canvas.getContext("2d");

ctx.fillRect(50,50,50,50); 

img.onload = function() {
    ctx.drawImage(img, 0, 0);
    var g = ctx.canvas.toDataURL("image/jpeg", 1);
    document.getElementById('test').value = g;
}