Javascript - 将图像保存到内部存储

Question

我从服务器下载图像为blob，然后将其转换为url并显示图像。

var nImageRequest = new XMLHttpRequest();
nImageRequest.open("POST", "http://xx.xx.xx.xxx/server/api/download_image.php", true);

nImageRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
nImageRequest.responseType = 'blob';

nImageRequest.onreadystatechange = function(oEvent) {

  if (nImageRequest.readyState == 4) {
    if (nImageRequest.status == 200) {

      var image = new Image();
      var url = window.URL || window.webkitURL;

      image.src = url.createObjectURL(nImageRequest.response);
      document.body.appendChild(image);

      // window.webkitRequestFileSystem(window.PERSISTENT , 1024*1024, SaveDatFileBro);
    }
  }
};

nImageRequest.send(imageFilename);

现在，我想将其存储在用户手机的内部存储空间中。如何使用javascript

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