jQuery window scroll fx to add or remove a class based on the div's position from top or bottom of the page.

jQuery Scroll to add or remove class

function activeToggle ($theDiv) {

    var divTop = $theDiv.offset().top - windowTop;

    if (divTop > cutoffTop && divTop < cutoffBottom ) { 
        $theDiv.addClass('active'); 
    }
    else { 
        $theDiv.removeClass('active');  
    }
}

$(window).scroll( function() {
    windowHeight = $(window).innerHeight();
    windowTop = $(window).scrollTop();
    cutoffTop = 20; // # is distance in pixels from top of page
    cutoffBottom = windowHeight - 360; // # is distance in pixels from bottom of page
    
    $('.theDiv').each( function( index ){
        activeToggle($(this));
    });
});