scroll-to-anchor.js

// Modified from https://stackoverflow.com/a/13067009
// Going for a JS solution to scrolling to an anchor so we can benefit from
// less hacky css and smooth scrolling.

var scrollToAnchor = {
  bind: function() {
    var document = window.document;
    var history = window.history;
    var location = window.location
    var HISTORY_SUPPORT = !!(history && history.pushState);

    var anchorScrolls = {
      ANCHOR_REGEX: /^#[^ ]+$/,
      offsetHeightPx: function() {
        return $(".header-holder").height() + 20;
      },

      /**
       * Establish events, and fix initial scroll position if a hash is provided.
       */
      init: function() {
        this.scrollToCurrent();
        $(window).on('hashchange', $.proxy(this, 'scrollToCurrent'));
        $('body').on('click', 'a', $.proxy(this, 'delegateAnchors'));
      },

      /**
       * Return the offset amount to deduct from the normal scroll position.
       * Modify as appropriate to allow for dynamic calculations
       */
      getFixedOffset: function() {
        return this.offsetHeightPx();
      },

      /**
       * If the provided href is an anchor which resolves to an element on the
       * page, scroll to it.
       * @param  {String} href
       * @return {Boolean} - Was the href an anchor.
       */
      scrollIfAnchor: function(href, pushToHistory) {
        var match, anchorOffset;

        if(!this.ANCHOR_REGEX.test(href)) {
          return false;
        }

        match = document.getElementById(href.slice(1));

        if(match) {
          anchorOffset = $(match).offset().top - this.getFixedOffset();
          $('html, body').scrollTop(anchorOffset);

          // Add the state to history as-per normal anchor links
          if(HISTORY_SUPPORT && pushToHistory) {
            history.pushState({}, document.title, location.pathname + href);
          }
        }

        return !!match;
      },

      /**
       * Attempt to scroll to the current location's hash.
       */
      scrollToCurrent: function(e) {
        if(this.scrollIfAnchor(window.location.hash) && e) {
          e.preventDefault();
        }
      },

      /**
       * If the click event's target was an anchor, fix the scroll position.
       */
      delegateAnchors: function(e) {
        var elem = e.target;

        if(this.scrollIfAnchor(elem.getAttribute('href'), true)) {
          e.preventDefault();
        }
      }
    };

    $(document).ready($.proxy(anchorScrolls, 'init'));
  }
};