select2 + twitter bootstrap

select2.js

var onscroll = function() {
    var open = $(".select2-drop.select2-drop-active.select2-with-searchbox");
    var originalTop = open.data('original-top');
    var top = originalTop || parseInt(open.css('top'), 10);
    if(!originalTop) {
      open.data('original-top', top);
    }

    //ajust top
    open.css('top', (top + $(window).scrollTop()) + 'px');
  };


  //keep track of scroll when modal is opend
  Modal.prototype.show = _.wrap(Modal.prototype.show, function(show, e) {
    $(window).on('scroll', onscroll);
    show.apply(this, [e]);
  });

  Modal.prototype.hide = _.wrap(Modal.prototype.hide, function(hide, e) {
    $(window).off('scroll', onscroll);
    hide.apply(this, [e]);
  });