title: FileReader.onprogress chunk size
body: <p>How does your browser decide how often to fire the <code>FileReader.onprogress</code> event? I'm doing some processing inside of this event and I think it's firing more often that I'd like. I want bigger chunks. Is there a way to tell it to fire less often?</p>
  
  <p>Sample code:</p>
  
  <pre><code>_.each(dropEvent.originalEvent.dataTransfer.files, function(file) {
      var reader = new FileReader();
      var pos = 0;
      var startTime = +new Date();
      var xxh = XXH();
  
      reader.onprogress = function(progress) {
          var length = progress.loaded - pos;
          var arr = new Uint8Array(reader.result, pos, length);
          pos += length;
  
          xxh.update(arr);
  
          if (progress.lengthComputable) {
              console.log('hashing', (progress.loaded / progress.total * 100).toFixed(1) + '%');
          }
      };
  
      reader.onload = function() {
          var arr = new Uint8Array(reader.result, pos);
          xxh.update(arr);
          var hash = xxh.digest().toNumber();
  
          var elapsed = +new Date() - startTime;
          console.info("computed hash", xxh.digest().toNumber(), 'for file', file.name, 'in', elapsed, 'ms');
      };
  
      reader.readAsArrayBuffer(file);
  });
  </code></pre>