[Wikitech-l] Ajax event firing for username validation in Extension: SignupAPI

Hi,

In SignupAPI extension, should I fire the Ajax user validation (username available & not illegal checking) 'onchange' / 'onkeyup' ?

1) 'onchange' would cause less Ajax calls but will give result only when the user has pressed tab or clicks to the next field

2) 'onkeyup' would cause a lot of Ajax calls but would give result as & when the user types so that he can correct the input if needed rather than going to the next field & then finding that he just gave some invalid input in the previous field

What would be better from a UX + Performance point of view? Is there any other JavaScript event I should be looking at?

Thanks Akshay