are there issues with javascript and browsers ?

[Jack]

Hello,

I am looking to make a client app. truly a thin web HTML client if
possible but still have some data validation done in the UI, so I
guess that makes my technology of choice javascript/DHTML - my
question is, what are the drawbacks of using javascript for web
applications ? I have heard it no longer is a thin client (but I dont
know how else to do it) and there are issues in that different kinds
of browsers dont necessarily all support it...

If anyone has any thoughts or additional issues javascript causes I
would appreciate the clarification and information..

Jack