Moment() vs predefined Moment() date
<p>I am a bit confused on how the Moment functions work (such as <code>startOf()</code>, <code>weekday()</code>, etc).</p>

<p>My question is: how do I obtain the start of the week from a predefined date?</p>

<p>Consider these two calls on <code>9/21/16</code>:</p>

<pre><code>moment().startOf('week') // Returns a moment object with date set to Sun Sep 18 2016 ...
</code></pre>

<p>vs</p>

<pre><code>moment(new Date("9/21/16")).startOf('week') // Returns a moment object with date set to Wed Sep 21 2016 ...
</code></pre>

<p>Why don't these behave in the same way? The same is true when using <code>weekday(0)</code> instead of <code>startOf('week')</code></p>