scrollToAnimated

scrollToAnimated

// scrollToAnimated
(function(window) {

  'use strict';

  // provides requestAnimationFrame in a cross browser way
  window.requestAnimFrame = (function() {
    'use strict';
    return window.requestAnimationFrame ||
      window.webkitRequestAnimationFrame ||
      window.mozRequestAnimationFrame ||
      window.oRequestAnimationFrame ||
      window.msRequestAnimationFrame ||
      function(callback, element) {
        return window.setTimeout(callback, 1000 / 60);
    };
  })();

  // ease
  Math.easeInOutQuad = function(t, b, c, d) {
    t /= d / 2;
    if (t < 1) {
      return c / 2 * t * t + b;
    }
    t--;
    return -c / 2 * (t * (t - 2) - 1) + b;
  };

  // scrollTo
  function scrollToAnimated(to, callback, duration) {
    var doc = document.body,
      start = doc.scrollTop,
      change = to - start,
      currentTime = 0,
      increment = 20,
      raf;

    duration = (typeof(duration) === 'undefined') ? 500 : duration;

    function animateScroll() {
      currentTime += increment;
      var val = Math.easeInOutQuad(currentTime, start, change, duration);
      doc.scrollTop = val;
      if (currentTime < duration) {
        raf = requestAnimFrame(animateScroll);
      } else {
        cancelAnimationFrame(raf);
        if (callback && typeof(callback) === 'function') {
          callback();
        }
      }
    }
    animateScroll();
  }

  // AMD Support
  if (typeof define === 'function' && define.amd)
    define(function() {
      return scrollToAnimated;
    });
  else
    window.scrollToAnimated = scrollToAnimated;

}(window));