skillful,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script>
window.onload = function () {
var id = "",
form = document.querySelector("form");
form.onsubmit = function (a) {
alert(id);
return !1
};
form.onclick = function (a) {
a = a.target || window.event.srcElement;
"INPUT" == a.tagName && (id = a.id)
}
};
</script>
</head>
<body>
<form action="" method="POST" >
<input name="kn1" id="kn1" value="Кнопка1" type="submit">
<input name="kn2" id="kn2" value="Кнопка2" type="submit">
</form>
</body>
</html>