navigation.js

/**
 * Takes the last slide and places it at the front.
 */
function goBack() {
  var wrapper = document.querySelector('#wrapper');
  var lastSlide = wrapper.lastChild;
  while (lastSlide != null && lastSlide.nodeType !== 1) {
    lastSlide = lastSlide.previousSibling;
  }

  wrapper.removeChild(lastSlide);
  wrapper.insertBefore(lastSlide, wrapper.firstChild);

  updateURL();
}

/**
 * Takes the first slide and places it at the end.
 */
function goForward() {
  var wrapper = document.querySelector('#wrapper');
  var firstSlide = wrapper.firstChild;
  while (firstSlide != null && firstSlide.nodeType !== 1) {
    firstSlide = firstSlide.nextSibling;
  }

  wrapper.removeChild(firstSlide);
  wrapper.appendChild(firstSlide);

  updateURL();
}

/**
 * Updates the current URL to include a hashtag of the current page number.
 */
function updateURL() {
  window.history.replaceState({} , null, '#' + currentPage());
}

/**
 * Returns the current page number of the presentation.
 */
function currentPage() {
  return document.querySelector('#wrapper .slide').dataset.page;
}

/**
 * Returns a NodeList of each .slide element.
 */
function allSlides() {
  return document.querySelectorAll('#wrapper .slide');
}

/**
 * Give each slide a "page" data attribute.
 */
function setPageNumbers() {
  var wrapper = document.querySelector('#wrapper');
  var pages   = wrapper.querySelectorAll('section');
  var page;

  for (var i = 0; i < pages.length; ++i) {
    page = pages[i];
    page.dataset.page = i;
  }
}

/**
 * Go to the specified page of content.
 */
function goToPage(page) {
  // Try to find the target slide.
  var targetSlide = document.querySelector('#wrapper .slide[data-page="' + page + '"]');

  // If it actually exists, go forward until we find it.
  if (targetSlide) {
    var numSlides = allSlides().length;

    for (var i = 0; currentPage() != page && i < numSlides; i++) {
      goForward();
    }
  }
}

window.onload = function () {

  // Give each slide a "page" data attribute.
  setPageNumbers();

  // If the location hash specifies a page number, go to it.
  var page = window.location.hash.slice(1);
  if (page) goToPage(page);

  document.onkeydown = function (e) {
    var kc = e.keyCode;

    // left, down, H, J, backspace - BACK
    // up, right, K, L, space, enter - FORWARD
    if (kc == 37 || kc == 40 || kc == 8 || kc == 72 || kc == 74) {
      goBack();
    } else if (kc == 38 || kc == 39 || kc == 13 || kc == 32 || kc == 75 || kc == 76) {
      goForward();
    }
  }

  if (document.querySelector('#next') && document.querySelector('#prev')) {
    document.querySelector('#next').onclick = function (e) {
      e.preventDefault();
      goForward();
    }

    document.querySelector('#prev').onclick = function (e) {
      e.preventDefault();
      goBack();
    }
  }

}