js/smooth-scroll.js

/**
 * smooth-scroll.js 1.0.0
 * Make your page scrolling smooth
 * Requires JQuery - Does not work with JQuery slim 
 * Based on https://css-tricks.com/snippets/jquery/smooth-scrolling/
 */

(function() {

  var duration = 500

  $('a[href*="#"]')
    // Remove links that don't actually link to anything
    .not('[href="#"]')
    .click(function(event) {
      // On-page links
      if (
        location.pathname.replace(/^\//, '') == this.pathname.replace(/^\//, '') 
        && 
        location.hostname == this.hostname
      ) {
        // Figure out element to scroll to
        var target = $(this.hash);
        target = target.length ? target : $('[name=' + this.hash.slice(1) + ']')
        // Does a scroll target exist?
        if (target.length) {
          // Only prevent default if animation is actually gonna happen
          event.preventDefault()
          
          $('html, body').animate({
            scrollTop: target.offset().top
          },
          duration, function() {
            // Callback after animation
            // Must change focus!
            var $target = $(target);
            $target.focus();
            if ($target.is(":focus")) { // Checking if the target was focused
              return false;
            } else {
              $target.attr('tabindex','-1'); // Adding tabindex for elements not focusable
              $target.focus(); // Set focus again
            };
          });
        }
      }
    });

})();