title: How to type check a Date object in flow?
body: <p>I have a function that takes a Date object as its paramater. I am not able to figure out how to annotate this. </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>function diffDate (start: any, end:any) {
  //....
  }</code></pre>
  </div>
  </div>
  
  How do I type annotate <code>start</code> and <code>end</code> as Date objects?</p>