title: base64 data URL to blob and then write file ionic
body: <p>i have converted canvas to data url.</p>
  
  <pre><code> var dataUrl = this._CANVAS.toDataURL('image/jpeg', 0.7);
  </code></pre>
  
  <p>how to convert dataURL to blob and then save it as a image file in app folder ionic.?</p>