Disable negative scroll in iOS

gistfile1.js

disableNegativeTouchScroll: function() {
  var initialY = null;
  var nodeStack = [];
  var $window = $(window);

  $window.bind('touchstart', function(e) {
    initialY = e.originalEvent.pageY;
    nodeStack = $(e.target).parents().andSelf().get().reverse();
    nodeStack = nodeStack.map(function(node) {
      return $(node);
    });
  });

  $window.bind('touchend touchcancel', function(e) {
    initialY = null;
    nodeStack = [];
  });

  $window.bind('touchmove', function(e) {

    if (!initialY) {
      e.preventDefault();
    }

    var direction = e.originalEvent.pageY - initialY;

    for (var i = 0; i < nodeStack.length; i +=1) {
      var $node = nodeStack[i];
      var nodeHeight = $node.height();
      var scrollHeight = $node[0].scrollHeight - 2;
      var nodeScrollTop = $node.scrollTop();

      if (scrollHeight > nodeHeight) {
        // the user is dragging the content up, and the element is already scrolled down a bit.
        var allowedUp = direction > 0 && nodeScrollTop > 0;

        // the user is dragging the content down, and the element is up a bit.
        var allowedDown = direction < 0 && nodeScrollTop < scrollHeight - nodeHeight;

        if (allowedUp || allowedDown) {
          return;
        }
      }
    }

    // disable drag
    e.preventDefault();
  });
}

Thanks!