What is event pooling in react? : <blockquote>
  <p>The SyntheticEvent is pooled. This means that the SyntheticEvent object will be reused and all properties will be nullified after the event callback has been invoked. This is for performance reasons. As such, you cannot access the event in an asynchronous way.</p>
</blockquote>

<p>refer : <a href="https://facebook.github.io/react/docs/events.html" rel="noreferrer">Event System in React</a></p>
