scrollHelper

gistfile1.js

var App = {};
App.enableSmoothScroll = function(){
  var lastScrollY= 0,
      isScrolling = false,
      targetAnc,
      startTouch = {},
      endTouch = {};

  function saveCurrentPos(e){
    lastScrollY = window.scrollY;
    startTouch = endTouch = e.originalEvent.targetTouches[0];
  }

  function saveMovedPos(e){
    endTouch = e.originalEvent.targetTouches[0];
  }

  function smoothScroll(e){
    var currentScrollY,direction,scroll;
    if (startTouch.pageY-endTouch.pageY < 10 &&
        startTouch.pageY-endTouch.pageY > -10){
      return;
    }
    currentScrollY = window.scrollY;
    direction = lastScrollY > currentScrollY ? -1 : 1;
  

    isScrolling = true;
    target = currentScrollY + (500 * direction);
    if (target < 0){
      target = 0;
    }
    $('html body').animate({scrollTop:target}, 200,function(){
      isScrolling = false;
    });
  }
  $(window).on('touchstart',saveCurrentPos);
  $(window).on('touchmove',saveMovedPos);
  $(window).on('touchend',smoothScroll);
};