Focus Trapping BITV

snippet.js

function trapFocus(element) {
    'use strict';
    var focusableEls = element.querySelectorAll('a[href]:not([disabled]), button:not([disabled]), textarea:not([disabled]), input[type="text"]:not([disabled]), input[type="radio"]:not([disabled]), input[type="checkbox"]:not([disabled]), select:not([disabled])');
    var firstFocusableEl = focusableEls[0];
    var lastFocusableEl = focusableEls[focusableEls.length - 1];
    var KEYCODE_TAB = 9;

    element.addEventListener('keydown', function (e) {
        var isTabPressed = (e.key === 'Tab' || e.keyCode === KEYCODE_TAB);

        if (!isTabPressed) {
            return;
        }

        if (e.shiftKey) /* shift + tab */ {
            if (document.activeElement === firstFocusableEl) {
                lastFocusableEl.focus();
                e.preventDefault();
            }
        } else /* tab */ {
            if (document.activeElement === lastFocusableEl) {
                firstFocusableEl.focus();
                e.preventDefault();
            }
        }
    });
}    

$('#header__offscreenToggler').on('click', function (e) {
        e.preventDefault();
        e.stopImmediatePropagation();
        openOffscreenWrapper();
        // keyboard
        if (e.detail === 0) {
            $('#offscreen__offscreenToggler').focus();
            trapFocus(document.getElementById('offscreen__wrapper'));
        }
    });