Why is object/associative array values not setting when I use $item.data("something").x
<p>Why is it when I do something like </p>

<p><a href="http://jsfiddle.net/sUhn9/" rel="nofollow">http://jsfiddle.net/sUhn9/</a></p>

<p><em>Added relevant HTML</em></p>

<pre><code>&lt;div id="container" data-physics='{x: 10, y: 5}'&gt;Hello&lt;/div&gt;
</code></pre>

<p>JavaScript:</p>

<pre><code>$(function() {
    var obj = $("#container").data("physics");
    console.log("b4", obj);
    obj.x = -2;
    obj.y = -6;
    console.log("after", obj);
});
</code></pre>

<p>I get </p>

<pre><code>b4 {x: 10, y: 5}
after {x: 10, y: 5}
</code></pre>

<p>Where x and y are not being set</p>
