Question: I want to animate a div from top down. I think the idea is animate the height from 0 to its rendered width.
But before it is shown I don't know the rendered width, how to write the code to animate this?

It's like: `$.animate({"width":"auto"})`

Answer: 
You need to grab the width using `.width()` like so:

```
var $el = $("#elementID");
$el.animate({height: $el.width()});

```
```
$("#elementID").animate({height:$(this).width()});

```