( function() {
    'use strict';

    if ( 'querySelector' in document && 'addEventListener' in window ) {
        const goTop = document.querySelector( '#go-to-top' );

        window.addEventListener( 'scroll', ()=> {
            if ( window.scrollY >= 50 ) {
                goTop.style.display = 'block';
            } else {
                goTop.style.display = 'none';
            }

        });

        goTop.addEventListener( 'click', ()=> {
            document.body.scrollTop = 0; // For Safari
            document.documentElement.scrollTop = 0; // For Chrome, Firefox, IE and Opera
        });
    }
} ) ();