How to move the calling function from onclick to onsubmit on aspx form ?

I have on my aspx page this form with standard button code which I copied from web:
<form id="form1"> <input type="text" name="Text1" required> <input type="submit" name="FileSelected" onclick="XXXX.uploadData(this.parentNode)"/> <form>
This code is working. However, onclick code bypasses the required validation. I want to move this code to the onsubmit event of the form.
I dunno what to use to replace "this.parentNode"
I tried
<form id="form1" onsubmit"XXXX.uploadData(FileSelected.parentNode)"/> <input type="text" name="Text1" required> <input type="submit" name="FileSelected" ID ="FileSelected" /> <form>
but it does not work. Please help.. thanks