Dencho,
может css хватит?
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
li{
position: relative;
}
li > .sub_menu {
display: none;
}
li:hover > .sub_menu {
display: block;
margin-left: 10px;
position: absolute;
top: 0px;
left: 10px;
}
</style>
<script>
</script>
</head>
<body>
<ul id="js_menu" class="js_menu">
<li class="item_el" id="id-el-1">item1</li>
<li class="item_el disabled" id="id-el-2">item2</li>
<li class="item_el" id="id-el-3">item3</li>
<li class="item_el has_sub_menu" id="id-el-4">item4
<ul class="sub_menu">
<li class="item_el" id="id-el-5">item1</li>
<li class="item_el has_sub_menu" id="id-el-6">item2
<ul class="sub_menu">
<li class="item_el" id="id-el-7">item1</li>
<li class="item_el" id="id-el-8">item2</li>
<li class="item_el" id="id-el-9">item3</li>
<li class="item_el" id="id-el-10">item4</li>
</ul>
</li>
<li class="item_el" id="id-el-11">item3</li>
<li class="item_el has_sub_menu" id="id-el-12">item4
<ul class="sub_menu">
<li class="item_el" id="id-el-13">item1</li>
<li class="item_el" id="id-el-14">item2</li>
<li class="item_el" id="id-el-15">item3</li>
<li class="item_el" id="id-el-16">item4</li>
</ul>
</li>
</ul>
</li>
</ul>
</body>
</html>