[jQuery] Form plug-in: problem with POST

[jQuery] Form plug-in: problem with POST


Here's a tricky one that no one on my other favorite javascript forums
where able to answer, so maybe the expert jQuery crew knows what's
going on:
My form:
<html>
<form id="myForm" action="functionLibrary.php?function=formSubmit">
<input type="submit" value="SEND FORM">
</form>
</html>
My javascript/jQuery:
<script>
$('#myForm').ajaxForm({
    type: "POST",
    success: showResponse
});
function showResponse(responseText, statusText) {
alert(responseText);
}
</script>
functionLibrary.php:
<?php
if(isset($_GET['fnc'])
eval($_GET['fnc'].'();');
function formSubmit(){
echo 'form submitted.';
}
?>
When ajaxForm has type= "POST", this DOES NOT work. It does not like
me using a function library with POST.
It DOES work when type="GET"
if action="formSubmit.php" instead, then ajaxForm DOES work with
EITHER POST or GET:
<?php
echo 'form submitted.';
?>
Why can't I use type="POST" with a function library as described in
functionLibrary.php?