Function isTabKey

src/components/ModalPortal.js:25–25

 * `react-modal` only supports React >18 (which dropped IE support).
 */
const isTabKey = event => event.code === "Tab" || event.keyCode === 9;
const isEscKey = event => event.code === "Escape" || event.keyCode === 27;

let ariaHiddenInstances = 0;