H5压缩图片上传质量，传入Image获取base64批量上传

function appUploadImage() {
    var width = 500; //图像大小
    var quality = 0.5; //图像质量
    var canvas = document.createElement("canvas");
    var drawer = canvas.getContext("2d");
    canvas.width = width;
    canvas.height = width * (img.height / img.width);
    drawer.drawImage(img, 0, 0, canvas.width, canvas.height);
    return canvas.toDataURL("image/png", quality);
}