affix

affix.js

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

processScroll()

$nav.on('click',
    function () {
            if (!isFixed) setTimeout(function () {  $win.scrollTop($win.scrollTop() - 47) }, 10)
})

$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')
        }
}