How to use Mouse Wheel for jumping to next or previous # section in html

Question

I have a site with top nav menu:

<nav id="menu">
    <ul id="menu-nav">
        <li class="current"><a href="#home-slider">Home</a></li>
        <li><a href="#Cakes">Cakes</a></li>
        <li><a href="#Candy">Candy</a></li>
        <li><a href="#Marshmellow">Marshmellow</a></li>
        <li><a href="#Honey">Honey</a></li>
     </ul>
 </nav>

And all my sections are:

<div id="Cakes" class="page">
    <div class="container">
        This is sweet
    </div>
</div>

How can I use the mouse wheel to jump directly to the next or previous section?

Currently the mouse wheel will scroll the page like normal. But I want it to jump to every section with one wheel rotation without scrolling all the entire page.

Answer 1

Without plugins, all we need to do is to capture the mousewheel using mousewheel event -on Firefox we use DOMMouseScroll instead- and depending on the value of the event's originalEvent.wheelDelta -again in Firefox it is originalEvent.detail, thanks Firefox- if this value is positive then the user is scrolling upward, if it's negative then the direction is down.

JS Fiddle 1

jQuery ⁽¹⁾ :

//initialize
var winHeight = $(window).height(),
    pages = $('.page'),
    navLinks = $('#menu-nav a'),
    currentPage = 0;

$('html, body').animate({ scrollTop: 0}, 0);

// listen to the mousewheel scroll       
$(window).on('mousewheel DOMMouseScroll', function(e){

    //by default set the direction to DOWN
    var direction = 'down',
    $th = $(this),
    // depending on the currentPage value we determine the page offset
    currentPageOffset = currentPage * winHeight;

    // if the value of these properties of the even is positive then the direction is UP
    if (e.originalEvent.wheelDelta > 0 || e.originalEvent.detail < 0) {
        direction = 'up';
    }

   // if the direction is DOWN and the currentPage increasing won't exceed
   // the number of PAGES divs, then we scroll downward and increase the value
   // of currentPage for further calculations.
   if(direction == 'down' && currentPage <= pages.length - 2){
       $th.scrollTop(currentPageOffset + winHeight);
       currentPage++;
   } else if(direction == 'up' && currentPage >= 0) {
       // else scroll up and decrease the value of currentPage IF the direction
       //  is UP and we're not on the very first slide
       $th.scrollTop(currentPageOffset - winHeight);
       currentPage--;
   }
});

// as final step we need to update the value of currenPage upon the clicking of the
// navbar links to insure having correct value of currentPage
navLinks.each(function(index){
    $(this).on('click', function(){
    navLinks.parent().removeClass('current');
    $(this).parent().addClass('current');
    currentPage = index;
  });
});

---

⁽¹⁾UPDATE

If you don't want to use jQuery, below is pure javascript code doing the same as above, this won't work in IE8 and below though:

JS Fiddle 2

Pure Javascript:

//initialize
var winHeight = window.innerHeight,
  pages = document.getElementsByClassName('page'),
  navLinks = document.querySelectorAll('#menu-nav a'),
  currentPage = 0;

window.addEventListener('mousewheel', function(e) {
  scrollPages(e.wheelDelta);
});
window.addEventListener('DOMMouseScroll', function(e) {
  scrollPages(-1 * e.detail);
});

function scrollPages(delta) {
  var direction = (delta > 0) ? 'up' : 'down',
    currentPageOffset = currentPage * winHeight;

  if (direction == 'down' && currentPage <= pages.length - 2) {
    window.scrollTo(0, currentPageOffset + winHeight);
    currentPage++;
  } else if (direction == 'up' && currentPage > 0) {
    window.scrollTo(0, currentPageOffset - winHeight);
    currentPage--;
  }
}

for (var i = 0; i < navLinks.length; i++) {
  navLinks[i].addEventListener('click', updateNav(i));
}

function updateNav(i) {
  return function() {
    for (var j = 0; j < navLinks.length; j++) {
      navLinks[j].parentNode.classList.remove('current');
    }
    navLinks[i].parentNode.classList.add('current');
    currentPage = i;
  }
}