title: keycode and charcode
body: <p>Why do people write statement like</p>
  
  <pre class="lang-js prettyprint-override"><code>e.keyCode ? e.keyCode : e.charCode
  </code></pre>
  
  <p>Some people also use <code>e.which</code></p>
  
  <p>Could someone please explain?</p>