图片链接转成base64

一半需要我的图像转换为base64字符串，这样我们可以把我的形象到服务器。现在我们提供一个js：

function convertImgToBase64(url, callback, outputFormat){var canvas = document.createElement('CANVAS'),
        ctx = canvas.getContext('2d'),
        img =newImage;
    img.crossOrigin ='Anonymous';
    img.onload =function(){
        canvas.height = img.height;
        canvas.width = img.width;
        ctx.drawImage(img,0,0);var dataURL = canvas.toDataURL(outputFormat ||'image/png');
        callback.call(this, dataURL);
        canvas =null;};
    img.src = url;}

convertImgToBase64('http://bit.ly/18g0VNp',function(base64Img){// Base64DataURL});