title: adding / subtracting time in JS
body: <p>Lately I was playing with JS and I found something interesting. That is what I wrote into chrome console:</p>
  
  <pre><code>today = new Date()
  -&gt; Mon Apr 29 2013 13:06:01 GMT+0200 (CEST)
  DAY = 1000 * 3600 * 24
  -&gt; 86400000
  today - 2 * DAY
  -&gt; 1367060761452
  today + 2 * DAY
  -&gt; "Mon Apr 29 2013 13:06:01 GMT+0200 (CEST)172800000"
  </code></pre>
  
  <p>And I am wondering why am I getting different types of answer depending on the type of operation - adding / subtracting. When I do something like that:</p>
  
  <pre><code>today - (-2) * DAY
  </code></pre>
  
  <p>everything is fine. Is there any ideology, or is it a bug?</p>