Example: detect scroll position and change navi style

navStyleChanger.js

// Navigationbar to be changed (cached here for performance, always grabbing
//                              it new in the scroll-callback is bad for performance)
var $navi = $('.myNav')

function changeNavStyle() {
    var top = (document.documentElement && document.documentElement.scrollTop) || document.body.scrollTop;

    if (top > 200) {
        $navi.addClass('.myNewStyle-Yo')
    } else {
        $navi.removeClass('.myNewStyle-Yo')
    }
}

// Call this once when the page loads, because the browser might restore the user
// to a scroll position where we need to change styles!
changeNavStyle()
// Actual scroll check
$(window).scroll(changeNavStyle)