Ask HN: Good Javascript learning exercise suggestions

Can you offer some suggestions of good Javascript exercises ? Both for beginner and advanced ?

I was thinking of a web based chat for advanced (this sounded a bit tricky that's why I picked it), and for something simple I had in mind tricks and animations for a form using jquery.

For books I had in mind :

http://www.amazon.com/JavaScript-Good-Parts-Douglas-Crockford/dp/0596517742/

http://www.amazon.com/exec/obidos/ASIN/0596101996/wrrrldwideweb

Thanks.