Using window.onload with Ubermenu

I am using a plugin to place this code on specific pages. But it is not firing correctly.

Has anyone had experience working with Ubermenu, WP and jQuery? Do I have to call jQuery into my <script></script> or should I scrap all this and go with through conditional tags?

Like this

<?php
$page = array( 42, 'page id', 'Page Title' );

if ( is_page($page) || is_single($post) ) {
?>
<script type="text/javascript">
window.onload=function(){$('#menu-item-156').mouseover(function(){
$(this).find('ul').slideDown();
});

$('#menu-item-156').trigger('mouseover');};
</script>
<?php  }  ?>