fixed widget on scroll

script.js

$(function() {
  if ($('#subs-wrapper').length) {
    sub_width = $('#subs-wrapper').parent('div').width()
    var el = $('#subs-wrapper');
    var stickyTop = $('#subs-wrapper').offset().top - 100;
    var stickyHeight = $('#subs-wrapper').height();
    screen_width = $(window).width();
    if ( 767 < screen_width){
      $(window).scroll(function() {
        var limit = $('#footer-top').offset().top - stickyHeight - 100;
        var windowTop = $(window).scrollTop();
        if (stickyTop < windowTop) {
          el.css({
            position: 'fixed',
            top: 35,
            width: sub_width
          });
        } else {
          el.css('position', 'static');
        }
        if (limit < windowTop) {
          var diff = limit - windowTop+35;
          el.css({
            top: diff
          });
        }
      });
    }
  }
});