title: React - key up event returns e.which as 0 while key down event returns correct key code
body: <p>For the past 2 days, I'm hell-bent on debugging an weird issue that happens only in iOS 7 devices.</p>
  
  <p>I have an React Input component, for which I have added an onKeyDown and onKeyUp event handlers.</p>
  
  <pre><code>&lt;input type='text' 
    defaultValue='hello' 
    onKeyDown={this.handleKeyDown} 
    onKeyUp={this.handleKeyUp} /&gt;
  
  function handleKeyDown(e){
    console.log('Key down event', e.which);
  }
  
  function handleKeyUp(e){
    console.log('Key up event', e.which);
  }
  </code></pre>
  
  <p>When I type in the characters, the key down event returns a proper key code but the key up event always returns 0. For example, if I press 'a', I am getting</p>
  
  <pre><code>Key down event 65
  Key up event 0
  </code></pre>
  
  <p>I guess, because of this, the characters I type are not showing up in the textbox.</p>
  
  <p>Any idea why it happens?</p>