Getting Event.target Attributes

I have a web form with several "submit" buttons.

One of these uploads a file, and I want to validate the user input
prior to submitting the form. I have an event handler specified with
the form's "onsubmit" attribute which checks the the
event.target.value to make sure the right submission type is being
evaluated.

When I try to get the target or srcElement value from the event
object, however, it is always "undefined".

Here is the cut-down version of the handler...

function validateIfUpload() {
if (window.event) {
evt = window.event
} else if (document.event) {
evt = document.event
}
if (evt.target) targ = evt.target
else if (evt.srcElement) targ = evt.srcElement
if (targ.nodeType == 3) // defeat Safari bug
targ = targ.parentNode
if (targ.value == "Upload") {
return validateUpload('prod_img_f')
}
return true
}