Minimalistic ScrollSpy

HTML

<ul id="top-menu">
    
    
    
    <li> <a href="http://google.co.nz">Google</a>

    </li>
    <li> <a href="http://domainname.com#foo">Foo</a>

    </li>
    <li> <a href="#bar">Bar</a>

    </li>
    <li> <a href="#baz">Baz</a>

    </li>
    

</ul>
<a id="foo">Foo</a>

<a id="bar">Bar</a>

<a id="baz">Baz</a>

CSS

body {
    height: 6000px;
    font-family: Helvetica, Arial;
}
#top-menu {
    position: fixed;
    z-index: 1;
    background: white;
    left: 0;
    right: 0;
    top: 0;
}
#top-menu li {
    float: left;
}
#top-menu a {
    display: block;
    padding: 5px 25px 7px 25px;
    width: 4em;
    text-align: center;
    -webkit-transition: .5s all ease-out;
    -moz-transition: .5s all ease-out;
    transition: .5s all ease-out;
    border-top: 3px solid white;
    color: #aaa;
    text-decoration: none;
}
#top-menu a:hover {
    color: #000;
}
#top-menu li.active a {
    border-top: 3px solid #333;
    color: #333;
}
#foo {
    position: absolute;
    top: 400px;
}
#bar {
    position: absolute;
    top: 800px;
}
#baz {
    position: absolute;
    top: 1200px;
}

JavaScript

// Cache selectors
var topMenu = $("#top-menu"),
    topMenuHeight = topMenu.outerHeight() + 15,
    // All list items
    //menuItems = topMenu.find("a"),
    menuItems = topMenu.find('a[href*=#]'),
    // Anchors corresponding to menu items
    scrollItems = menuItems.map(function () {
        var item = $('#' + $(this).attr('href').split('#')[1]);
        if (item.length) {
            return item;
        }
    });

// Bind to scroll
$(window).scroll(function () {
    // Get container scroll position
    var fromTop = $(this).scrollTop() + topMenuHeight;

    // Get id of current scroll item
    var cur = scrollItems.map(function () {
        if ($(this).offset().top < fromTop) return this;
    });
    // Get the id of the current element
    cur = cur[cur.length - 1];
    var id = cur && cur.length ? cur[0].id : "";
    // Set/remove active class
    menuItems.parent().removeClass("active")
        .end().filter("[href$=" + id + "]").parent().addClass("active");
});