$( document ).ready( function () {

    document.addEventListener( 'scroll', scrolled );

    let revealables = document.querySelectorAll( '.reveal' );

    let currentlyShowing = Math.floor( window.scrollY / ( window.innerHeight / revealables.length + 50 ) );


    for ( let i = 0; i < currentlyShowing; i++ ) {
        if ( i < parseInt( revealables.length ) ) {
            revealables[ i ].classList.add( 'active' );
        }
    }

    function scrolled() {
        let regPos = Math.floor( window.scrollY / ( window.innerHeight / revealables.length + 50 ) );
        if ( regPos < currentlyShowing && regPos < parseInt( revealables.length ) ) {
            revealables[ regPos ].classList.remove( 'active' );
        } else if ( regPos > currentlyShowing && regPos < parseInt( revealables.length ) + 1 ) {
            revealables[ currentlyShowing ].classList.add( 'active' );
        }
        currentlyShowing = regPos;
    }
} );