jQuery plugin to smoothly scroll the page when a link referencing an element ID is clicked.

smooth.jquery.js

/* smooth.jquery.js (ver 1.0.3)
 * by Matheus Pratta (http://matheus.io)
 * Requires: jQuery
 * Optional: jQuery UI (for animations other than 'linear' and 'swing') - required by default
 */

// Thanks Sebastien Lorber for this snippet
function canonicalize (url) {
    var div = document.createElement('div');
    div.innerHTML = '<a></a>';
    div.firstChild.href = url; // Ensures that the href is properly escaped
    div.innerHTML = div.innerHTML; // Run the current innerHTML back through the parser
    return div.firstChild.href;
}

var smooth_scroll_default_easing = (jQuery.effects) ? 'easeInOutExpo' : 'swing'; // Default easing, dafaults to jQueryUI first, but can also run only on jQuery.

function smooth_scroll_position(element) {
  var pos = $('html, body').scrollTop();
  if(pos == 0) pos = $('body').scrollTop(); // Additional check, in case of Safari or Chrome

  var els = [];

  if(element) {
    $('*').each(function(i, o) {
      var visible = true;

      if($(o).css('display') == 'none') visible = false;

      if(Math.floor($(o).offset().top) == Math.floor(pos) && visible) els = els.concat(o);
    });
  }

  if(els.length > 0) return $(els);
  
  return pos;
}

function smooth_scroll_to(element, duration, easing) {
  duration = duration || 1500;
  easing = easing || smooth_scroll_default_easing;

  $('html, body').stop().animate({
     scrollTop: $(element).offset().top
  }, duration, easing);
}

$(document).ready(function() {
  $("a[href*=#]").click(function(e) {
      var targ = canonicalize($(this).attr('href'));
      var targ_id = targ.substring(targ.indexOf('#'));
      var pos = targ.indexOf('#');
      if(~pos) {
        var url = targ.substring(0, pos);
        var curl = document.location.href;
        var cpos = curl.indexOf('#');
        if(~cpos) curl = curl.substring(0, cpos);
        if(curl == url) {
          e.preventDefault();

          var targ_element = $(targ_id);
          smooth_scroll_to(targ_element);
        }
      }
  });
});

Update (2015-0819): ver 1.0.2

• By default it can now run without jQueryUI. It will fallback to jQuery's "swing" easing then.

Update (2015-12-03): ver 1.0.3

• Added support to absolute URLs (it will know when you click a URL in same page)
• Added 'canonize' function to resolve URLs (thanks Sebastien Lorber)