title: Typescript date subtraction results in 0 instead of actual difference in time.
body: <p>I have two date objects Date in the form of </p>
  
  <pre><code>let t1 = 2015-03-26T09:43:39.504
  let t2 = 2015-03-26T10:43:39.504 
  </code></pre>
  
  <p>(These two times are retrieved by calling an API REST call). </p>
  
  <p>How would I get the difference in time between the two (in the form of seconds)? </p>
  
  <p>I've tried doing t1-t2 but the result is always 0. </p>