Scroll to anchor (active class)

Simple script (scrollspy)

by 8ogdan

HTML

<ul id="top-menu">
  <li class="active">
    <a href="#">Segment 1</a>
  </li>
  <li>
    <a href="#segment2">Segment 2</a>
  </li>
  <li>
    <a href="#segment3">Segment 3</a>
  </li>
  <li>
    <a href="#segment4">Segment 4</a>
  </li>
</ul>

<a id="segment2">Segment 2</a>

<a id="segment3">Segment 3</a>

<a id="segment4">Segment 4</a>

CSS

body {
    height: 6000px;
    font-family: Helvetica, Arial;
}

#top-menu {
    position: fixed;
    z-index: 1;
    background: white;
    left: 0;
    right: 0;
    top: 0;
    background-color: #42bdc2;
}

#top-menu li {
    float: left;
}

#top-menu a {
    display: block;
    padding: 15px 25px 17px 25px;
    width: 5em;
    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;
    text-decoration: none;
    color: #fff;
}

#top-menu a:hover {
    color: #000;
}

#top-menu li.active a {
    border-top: 3px solid #333;
    color: #333;
}

#segment2 {
    position: absolute;
    top: 400px;
}

#segment3 {
    position: absolute;
    top: 800px;
}

#segment4 {
    position: absolute;
    top: 1200px;
}

JavaScript

// Cache selectors
var lastId,
    topMenu = $("#top-menu"),
    topMenuHeight = topMenu.outerHeight()+15,
    // All list items
    menuItems = topMenu.find("a"),
    // Anchors corresponding to menu items
    scrollItems = menuItems.map(function(){
    	var temp = $(this).attr("href");
      console.log('temp', temp );
      var ID = temp.split('#').pop();
      console.log('ID', ID );
     	if(!ID){
      	console.log('ID undefined');
      	var item = $('body');
      } else {
      	var item = $('#'+ID);
      }
      
      console.log('item', item );
      if (item.length) { return item; }
    });

// Bind click handler to menu items
// so we can get a fancy scroll animation
menuItems.click(function(e){
  var href = $(this).attr("href"),
      offsetTop = href === "#" ? 0 : $(href).offset().top-topMenuHeight+1;
  $('html, body').stop().animate({ 
      scrollTop: offsetTop
  }, 300);
  e.preventDefault();
});

// 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 : "";
   
   if (lastId !== id) {
       lastId = id;
       // Set/remove active class
       menuItems
         .parent().removeClass("active")
         .end().filter("[href='#"+id+"']").parent().addClass("active");
   }                   
});