Maybe when dropdownlist is not visible it's a problem, but even when dropdown list is visible, the requiredfieldvalidator seems to just ignore the fact that it's empty and let's the user press buttons.
I have requiredfieldvalidators for my textboxes on the same page and they work perfectly.
It can be "Select One" that force the user to select one item from the dropdown list. Then you have to select a day for entering classes.
You have to check both years are selected and to date must greater than the from date. In such situation you can use three select boxes to enter birthday. This is a simple validation script that checks if the user has correctly entered his/her birthday.
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From all the examples above we see how to validate the form data using Java Script.
I hope this article is useful for all students and beginners.