title: FileReader.readAsArrayBuffer return is null
body: <p>I am following Html5rocks tutorial </p>
  
  <p><a href="http://www.html5rocks.com/en/tutorials/file/dndfiles/" rel="nofollow">http://www.html5rocks.com/en/tutorials/file/dndfiles/</a></p>
  
  <p>and I am trying to use readAsArrayBuffer instead of readAsBinaryString in slicing a file example (because I want to read gif header to find file resolution). But I am stuck because  evt.target.result (while using readAsBinaryString it is a string)</p>
  
  <p>any ideas?</p>
  
  <p>EDIT : Code </p>
  
  <pre><code>reader.onloadend = function(evt) 
  
  {
  
    if (evt.target.readyState == FileReader.DONE) { // DONE == 2
      document.getElementById('byte_content').textContent = evt.target.result;
      console.log(evt.target.result.byteLenght)
      document.getElementById('byte_range').textContent = 
          ['Read bytes: ', start + 1, ' - ', stop + 1,
           ' of ', file.size, ' byte file'].join('');
    }
  };
  
  if (file.webkitSlice) {
    var blob = file.webkitSlice(start, stop + 1);
  } else if (file.mozSlice) {
    var blob = file.mozSlice(start, stop + 1);
  }
  reader.readAsArrayBuffer(blob);
  }
  </code></pre>
  
  <p>so in Firefox 13 I get on screen : [object ArrayBuffer]</p>
  
  <p>and on console log : undefined</p>
  
  <p>while in Chromium 18 I get on console : Uncaught TypeError: Cannot read property 'byteLenght' of null  </p>