Empty field prevention...pop-ups possible?

[EnderX]

There's probably a simple solution to this, I simply don't know what it is.

I'm working on a php-driven web form, information to be submitted to a database. A number of the fields on the form correspond to not null areas in the db, so I need to figure out a way to prevent the end user from leaving those areas blank.

In the past, I've run into this problem in the Delphi programming environment. There, my solution was to create a pop-up dialog box warning the user that they had to fill in the required fields, and preventing the information from processing until they had done so.

I know I can refuse to process my data in the php file, since I'm drawing it from the form's data and validating it (currently against injection attacks, more as what I need becomes clearer) before doing anything else. But the form itself is supposed to run in the background; after finishing its work, the forms are supposed to redisplay, without any delay. Having to show the warning on the page would cause a few problems, and would also tend to make it look bad, as far as I can tell.

Is there some way I can create a 'pop-up' or equivalent warning box to let the end-user know that they've neglected to fill in a required field, like I'm used to in Delphi? Or is there some other, relatively simple, measure I could use to warn them about the fields? I'm not sure that simply marking the required fields will help; I've had trouble on both sides of that issue in the past. (Marked fields that wouldn't let me enter data, and fields that were required but not obviously so on a marked field form. And, of course, simple end-user [me] situational blindness.)

Any suggestions along these lines would be greatly appreciated.

Thanks in advance,
-EnderX

[stymiee]

You'll need JavaScript for this as PHP only works on the server. Once the page is loaded in the browser PHP no longer can interact with it.

[Puckdropper]

Javascript is probably your best bet here. You can do non-null validation in PHP, but you run in to problems with making the user go back to the form again.

[Rhyan]

In case you are not using Dreamweaver, you will have to javascript the validation code yourself, otherwise, dreamweaver has a validation script that you can apply to any form. It is really simple to add it to any existing form.
Make sure to make the required fields clearly marked - for example add a small * near the name to indicate a required field. Users are already experienced in filling forms, so this is a sign they won't miss if seen. However you cannot rely on user's attention. That's why javascript is your best solution.

p.s. You can find a sample validation code here http://w3schools.com/js/tryit.asp?filename=tryjs_formvalidate