JavaScript that can stop processing

[ryan headley]

I have a webapp running in Apache and Tomcat using JSPs, Servlets, and Java Beans. I also use some javascript to do some error checking before submit is clicked.
What I need to do is if there is an error in the form upon either clicking save, hitting enter, or tabbing out, popup an alert telling them there is an issue.
However, even when the click submit, the error pops up but the submit process still takes place. Is there a way to get that to stop??
Thanx

[ryan headley]

Nevermind, I got it to work.
I needed to do this: (this is general code not my code exactly)

<form onSubmit="return callFunction()">

Then in my code, if the test failed the function had to return false, else it returned true.
Problem solved...