Please explain why and how +new Date(); works as 'workaround' for Date.now() in IE8 or below
<p>(I'm reading the book "<em>Professional JavaScript for Web Developers</em>" to give a context about this question, specifically Chapter 5 on Reference Types) </p>

<p>I'm wondering why and how
<code>var start = +new Date();</code> works to get the current millisecond representation of now as a work-around to browsers (e.g.: IE8) that don't support ECMAScript 5's <code>Date.now()</code>?</p>

<p>What does the <code>+</code> operator do here compared to just plain old <code>new Date()</code> which also gets the current date and time?</p>
