Why `display = "none"` not works when button is clicked in [jsFiddle](http://jsfiddle.net/pUeue/3441/)?

**HTML:**

```
<div>This is a visible heading<div>
<div class="hidden">This is a hidden heading</div>
<div>Notice that the hidden heading still takes up space.</div>

<hr/>

```

**JavaScript:**

```
$('input[type=button]').click( function() {
 document.getElementsByClassName("hidden").style.display = "none";
});

```