prevent form submission until field is correct?

[partha]

I just want my users to be required to enter a valid email address before the form is submitted.

The function to validate an email address is easy and I know about onSubmit="" to make that function run before the form is submitted. But it just pops up an alert saying to enter a valid email address and then continues to submit the form!

How do I CANCEL the form submission if the email address entered is INVALID so the user can then enter a valid one?

[Dijkgraaf]

Usually you would have something like
<form name="test" onsubmit="return validate();">
and your validate function would return true if everything is OK, but false if something was wrong. Note the return in front of the function in the onsubmit :-)

[rocknbil]

Or just add onSubmit="return false;" to the form action tag.