writing a function to verify data inputted in textboxes

Although I've read and read information on javascript, I still can't put together a function that checks to make sure the correct data is being inputted in some textboxes.

I have five textboxes that I've created in ASP but now need to create a script that can verify whether the user inputted data or not. Can anyone guide me on how I can set this up?

There is a textbox that requires "numbers" only, when I place "string characters" in the box, it errors out. How can I avoid this from happening?

Thanks in advance.

Sounds like you might want to look at regular expressions. A bit cryptic, but may be just what your looking for if you want to check for certain characters. Also if your using input boxes, they are strings automatically and you may have to use parseInt() to make them integers.