Validate Individual Text Field Validation On Form?

I have written a form in HTML which contains username,lastname,email,password and submit.I have written a javascript to validate this form [validate(username,lastname,,password)].On submit this javascript function will be called and hence form get validated. I am passing all the arguements(username,lastname,email and password) to the javascript function..Is it possible to make me a code such that it should call an individual function for each field in the form.for ex:if i have not entered username, last name in the form and attempt to submit, only username arguement should be passed to the function as it comes first in the form.In other sense i want to validate individual text field validation of my form.