image转换为base64位

function getBase64(url){
        var Img = document.createElement('img');
        Img.src=url;
        var canvas = document.createElement("canvas"), //创建canvas元素
        width=Img.width, //确保canvas的尺寸和图片一样
        height=Img.height;
        canvas.width=width;
        canvas.height=height;
        canvas.getContext("2d").drawImage(Img,0,0,width,height); //将图片绘制到canvas中
        dataURL=canvas.toDataURL('image/jpeg'); //转换图片为dataURL
    }