Javascript map with two values in the key
<p>I have 3 dropdowns on my page, the options in the 3rd dropdown depend on the choices in the first two dropdowns. </p>

<p>So I am wondering if there is a way to implement a map in javaScript with a 2-dimensional key? Like <code>&lt;Key1, Key2&gt; -&gt; Value</code>. </p>

<p>I think an easy way is to concatenate two keys into one string. Is there any way that is more decent?</p>

<p>Thanks.</p>
