RE: Gridview textbox has data check without postback.. javascript?

I have a gridview with a textbox. I can set the textbox to
autopostback and check for a value in a prerender event to decide if I
should make a button on the grid row visible. However, the problem
with autopostback on a textbox is the postback occurrs when you select
another control or click away ( I guess). This is very awkward when
the control selected is dropdown as the page/selected control apears
to flicker and show and then retract the dropdownlist.

What's the best way to attack this? .. I want a button on my gridview
row to be visible when both a textbox and dropdown on  the control
have data selected/entered. problem is, I don't want to turn
autopostback on the textbox since it behalves awkwardly when the next
control selected is a dropdown and that cause a postback before I can
even select a value.

Thanks in advance for any help or information.