I am afraid that I really do not understand you - I am as confused as you claim to be!
You say "lots of functions to validate the form". But it is sensible to have only one (which may indeed call other functions en route).
One more time -
<form name = "whatever" action = "something" .......... onsubmit = "return validate()">
where vaidate() is the name of the function
(not the file) you wish to execute.