Highlight Menu Item when section is in viewport

<script>
( function( $ ) {
    $( document ).ready( function() {
        var homepageLinks = $( '#menu-main-menu-desktoptablet .homepage-item' ),
            lastId,
            topMenu = $( '#menu-main-menu-desktoptablet' ),
            topMenuHeight = topMenu.outerHeight() + 1,
            menuItems = topMenu.find( '.homepage-item a' ),
            scrollItems = menuItems.map( function() {
                var item = $($( this ).attr( 'href' ));
                if ( item.length ) { return item; }
            } );

        console.log(scrollItems );

        if ( $( 'body' ).hasClass( 'home' ) ) {
            homepageLinks.each( function() {
                var link = $( this ).find( 'a' );
                $( this ).removeClass( 'current-menu-item' );
                $( '#menu-main-menu-desktoptablet .home-item' ).addClass( 'current-menu-item' );
                link.click( function() {
                    homepageLinks.removeClass( 'current-menu-item' );
                    $( this ).parent().addClass( 'current-menu-item' );
                } )
            } );

            // Bind to scroll
            $( window ).scroll( function() {
                // Get container scroll position
                var fromTop = $( this ).scrollTop() + topMenuHeight;

                // Get id of current scroll item
                var cur = scrollItems.map( function() {
                    if ( $( this ).offset().top < fromTop )
                        return this;
                } );

                // Get the id of the current element
                cur = cur[ cur.length - 1 ];
                var id = cur && cur.length ? cur[ 0 ].id : '';

                if ( lastId !== id ) {
                    lastId = id;
                    // Set/remove active class
                    menuItems
                        .parent().removeClass( 'current-menu-item' )
                        .end().filter( '[href="#' + id + '"]' ).parent().addClass( 'current-menu-item' );
                }
            } );
        }
    } );
} )( jQuery );
</script>