title: dart upload file input type file
body: <p>Using Dart and Golang for a small app and looking to upload a file to server. </p>
  
  <p>Found something like this and placed it in my .dart file:</p>
  
  <pre><code>InputElement uploadInput = query('#file'); // my input type file
  
    uploadInput.on.change.add((e) {
      // read file content as dataURL
      final files = uploadInput.files;
      if (files.length == 1) {
        final file = files[0];
        final reader = new FileReader();
        reader.on.load.add((e) {
         sendDatas(reader.result);
        });
        reader.readAsDataURL(file);
      }
    });
  </code></pre>
  
  <p>but getting the following error:</p>
  
  <pre><code>Uncaught TypeError: Cannot read property 'get$on' of null 
  </code></pre>
  
  <p>any idea how to handle this? </p>
  
  <p>my goal: using input type file upload file to server (file size, &lt; 1MB)</p>