Assumes jQuery. Simply use class slide for any anchor to move to an ID, eg. <a href="#home" class="slide">Back to top</a>. Adjust duration for length of time. You could also do some math on the duration to make the speed constant based on distance. Remove "return false;" if you want to hashtag to show on the URL.

animate-to-object.js

$(document).ready(function() { 
  $(".slide").click(function() {
    $("html, body").animate({
      scrollTop: $($(this).attr("href")).offset().top + "px"
    }, {
      duration: 500,
      easing: "swing"
    });
    return false;
  });
});