var theForm = document.forms['form1'];
if (!theForm) {
theForm = document.form1;
}
function __doPostBack(eventTarget, eventArgument) {
if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
theForm.__EVENTTARGET.value = eventTarget;
theForm.__EVENTARGUMENT.value = eventArgument;
theForm.submit();
}
}

if (<span style="color:#006600">!theForm.onsubmit || (theForm.onsubmit() != false</span>)) {
...
}

$("form:first")<span style="color:#006600">.get(0)</span>.onsubmit = function () {
...
};