JS to make .subnav sticky

application.js

!function ($) {

  $(function(){

    // fix sub nav on scroll
    var $win = $(window)
      , $nav = $('.subnav')
      , navTop = $('.subnav').length && $('.subnav').offset().top - 40
      , isFixed = 0

    processScroll()

    $win.on('scroll', processScroll)

    function processScroll() {
      var i, scrollTop = $win.scrollTop()
      if (scrollTop >= navTop && !isFixed) {
        isFixed = 1
        $nav.addClass('subnav-fixed')
      } else if (scrollTop <= navTop && isFixed) {
        isFixed = 0
        $nav.removeClass('subnav-fixed')
      }
    }
})

}(window.jQuery)