Progressively enhanced cross-browser scrolling, via Modernizr, jQuery Transit, and classic $.scrollTo fallback

windowScroll.js

var sliding = false; // variable outside function scope to detect a slide is in progress

function slideTo(target, duration){ // credit to Mahieddine Abdelkader & Ludwig Wendzich for original ideas.
    var to = isNaN(target) ? $(target).offset().top : target, //find scroll to position
        from = $(window).scrollTop() //find starting point
        dy = to-from, //calculate change in scroll position - deltaY
        body = $("body"), // TODO: better to have it outside of local scope already rather than fetching it every time...
        duration = isNaN(duration) ? 500 : duration;

  // We're going to use translate-y to move the the page so it feels like we're at the *from* scroll position, when we're actually instantly at the *to* scroll position. */
        
      if(sliding){
        // if already sliding, keep on animating towards translate-y: 0 & reset scrollTop.
        // Might cause some jump.
        $(window).scrollTop(to);
      } else {
        body.css({y: dy});
        $(window).scrollTop(to);
        body.transition({
          y: 0,
          duration: duration,
          complete: function(){
            body.css("transition", "none"); // reset transition (may be managed by transit; but doesn't hurt to do it explicitly)
            sliding = false; // toggle
          }
        });
        sliding = true; // toggle
      
      }
      
}

function windowScroll(target, duration){
    duration = isNaN(duration) ? 500 : duration;
    if(Modernizr.csstransitions && Modernizr.csstransforms){ // test for requisite CSS3 features
      slideTo(target, duration);
    } else { // fallback to $.scrollTo
      var to = isNaN(target) ? target : {top: target, left: "+=0"};
        $.scrollTo(target, {duration: duration});
    }
}

$('#slideTop').on('click', function(){windowScroll(0, 2000);});

Dependencies

jQuery
Modernizr
jQuery scrollTo Plugin
//cdnjs.cloudflare.com/ajax/libs/jquery-scrollTo/1.4.3/jquery.scrollTo.min.js
jQuery Transit plugin
//cdnjs.cloudflare.com/ajax/libs/jquery.transit/0.9.9/jquery.transit.min.js