I have a react component that needs to know its dimensions ahead of time, **before it renders itself.**

When I'd make a widget in jquery I could just `$('#container').width()` and get the width of the container ahead of time when I build my component.

```
<div id='container'></div>

```

these container's dimensions are defined in CSS, along with a bunch of other containers on the page. who defines the height and width and placement of the components in React? I'm used to CSS doing that and being able to access that. But in React it seems I can only access that information after the component has rendered.