Jquery HTML2CANVAS未在IOS中下载

jQuery：

如何在IOS中下载图像？它在Windows中工作，但在iOS中不工作，我如何解决它

$( document ).ready(function() {
    html2canvas($('#image'), 
    {
      background: '#fff',
      onrendered: function (canvas) {
        var a = document.createElement('a');
        // toDataURL defaults to png, so we need to request a jpeg, then convert for file download.
        if(/(iPad|iPhone|iPod)/g.test(navigator.userAgent)){
            alert("Instructions...");
            a.target = "_blank";
            a.href = dataURL;
        }
        else{
          a.href = canvas.toDataURL("image/jpeg").replace("image/jpeg", "image/octet-stream");
          a.download = 'Release_order.jpg';
          a.click();
        }
      }
    });
});