What is this in javascript: "var var1 = var1 || []"
<p>I just want to increase my core javascript knowledge.</p>

<p>Sometimes I see this statement but I don't know what it does:</p>

<pre><code>var var1 = var1 || [];
</code></pre>

<p>What does it means and/or what's it for, and how do you use it?</p>

<p>Thank you.</p>
