jqform

<?php
if ( $_POST['bla'] ) {
    // do things
}
?>
<form id="jqform" action="bla.php" method="post">
    <input type="text" name="bla">
    <button type="submit">Submit!</button>
</form>

<script>
    $( '#jqform' ).submit( function() {
        var actions = $( '#jqform' ).attr( 'action' );
        $.post( actions, $( '#jqform' ).serialize(), function( data ) {
            // results here
        });
        return false;
    });
</script>