how to set day number to a date variable in mongo
<p>I have this variable in mongo</p>

<pre><code>var f_date = new Date();
</code></pre>

<p>and I want to modify f_date's day to 1st day, I was thinking of something like</p>

<pre><code>f_date.setDay(1);
</code></pre>

<p>how to do that???</p>