图片转Base64

原：https://www.cnblogs.com/mr-wuxiansheng/p/6931077.html

• image2Base64

function image2Base64(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;
}