HTMLFormElement.prototype.real_submit = HTMLFormElement.prototype.submit;
HTMLFormElement.prototype.submit = test2;

window.addEventListener('submit', function(e) {
                e.stopPropagation();
	e.preventDefault();
	test2(e);
}, true);

function test2(e) {
var frm = e ? e.target : this;

if (!test_onsubmit(frm)) { return false; }
var answer=confirm("blablablabla");
	if (answer) {
                                alert("Yes");
		this.real_submit();
		} else {
		alert("No");
		return false;
	}
}

function test_onsubmit(f) {
	alert(f.onsubmit);
	return !f.onsubmit || f.onsubmit();
}