title: RNFetchBlob.fs.writeFile how get notification on complete (NOT ALERT MESSAGE)
body: <p>How to notifiy the user on success the file write.</p>
  
  <pre><code>RNFetchBlob.fs.writeFile(path, Base64Code[1], 'base64')
          .then(res =&gt; {
              console.log(res);
              if (res &gt; 0) {
                  alert('download_success');
              } else {
                  alert('download_failed');
              }
          });
  </code></pre>