form submit jquery v javascript difference

in javascript this works fine and the validateForm function fires

ContactForm = document.getElementById('EmailForm');
ContactForm.onsubmit=validateForm;

function validateForm() {
   //do stuff here
}

but why doesnt a similar implementation of the same code in jquery not work? This is what I would like to do

ContactForm = $('#EmailForm');
ContactForm.submit=validateForm;

function validateForm() {
   //do stuff here
}

after reading http://api.jquery.com/submit/ the following code works

ContactForm = $('#EmailForm');
ContactForm.submit(function() {
   //do stuff here
});

why does the submit method require a function to wrap around the code im trying to fire. why can i not just call the function directly as native javascript does??

thanks in advance

Answer

Because jquery objects are wrapper around javascript objects. And jquery objects expose another set of methods to work with the underlying javascript objects. onsubmit is a property of the underlying javacript object, but jquery object does not have it. When you call

ContactForm.submit(function() {
   //do stuff here
});

The submit function of the jquery object will register the submit event for the underlying javascript object