(function (window, document) {
    'use strict';

    let className = 'tabbing';

    let handleFirstTab = function (e) {
        if (e.keyCode === 9) {
            document.body.classList.add(className);
            window.removeEventListener('keydown', handleFirstTab);
            window.addEventListener('mousedown', handleMouseDownOnce);
        }
    }

    let handleMouseDownOnce = function () {
        document.body.classList.remove(className);
        window.removeEventListener('mousedown', handleMouseDownOnce);
        window.addEventListener('keydown', handleFirstTab);
    }

    window.addEventListener('keydown', handleFirstTab);

})(window, document);