图片转base64

var img = "http://xxx/timg.jpg";
var image = new Image();
image.src = img;
image.onload = function() {
    //文件的Base64字符串
    var base64 = getBase64Image(image);
    console.log(base64);
}
/**
 * 图像转Base64
 */
function getBase64Image(img) {
    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 ext = img.src.substring(img.src.lastIndexOf(".") + 1).toLowerCase();
    var dataURL = canvas.toDataURL("image/" + ext);
    return dataURL;
}