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: 
using .width() will not return the full computed width including the border/padding etc... for this purpose i would use .outerWidth() and pass the optional true to include the margins.

```
$('element').animate({height: $('element').outerWidth(true)});

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

```