+/**
+ * Handle common keyboard navigation events within a given container.
+ */
+export class KeyboardNavigationHandler {
+
+ /**
+ * @param {Element} container
+ * @param {Function|null} onEscape
+ * @param {Function|null} onEnter
+ */
+ constructor(container, onEscape = null, onEnter = null) {
+ this.containers = [container];
+ this.onEscape = onEscape;
+ this.onEnter = onEnter;
+ container.addEventListener('keydown', this.#keydownHandler.bind(this));
+ }
+
+ /**
+ * Also share the keyboard event handling to the given element.
+ * Only elements within the original container are considered focusable though.
+ * @param {Element} element
+ */
+ shareHandlingToEl(element) {
+ this.containers.push(element);
+ element.addEventListener('keydown', this.#keydownHandler.bind(this));
+ }
+
+ /**
+ * Focus on the next focusable element within the current containers.
+ */
+ focusNext() {
+ const focusable = this.#getFocusable();
+ const currentIndex = focusable.indexOf(document.activeElement);
+ let newIndex = currentIndex + 1;
+ if (newIndex >= focusable.length) {
+ newIndex = 0;
+ }
+
+ focusable[newIndex].focus();
+ }
+
+ /**
+ * Focus on the previous existing focusable element within the current containers.
+ */
+ focusPrevious() {
+ const focusable = this.#getFocusable();
+ const currentIndex = focusable.indexOf(document.activeElement);
+ let newIndex = currentIndex - 1;
+ if (newIndex < 0) {
+ newIndex = focusable.length - 1;
+ }
+
+ focusable[newIndex].focus();
+ }
+
+ /**
+ * @param {KeyboardEvent} event
+ */
+ #keydownHandler(event) {
+ if (event.key === 'ArrowDown' || event.key === 'ArrowRight') {
+ this.focusNext();
+ event.preventDefault();
+ } else if (event.key === 'ArrowUp' || event.key === 'ArrowLeft') {
+ this.focusPrevious();
+ event.preventDefault();
+ } else if (event.key === 'Escape') {
+ if (this.onEscape) {
+ this.onEscape(event);
+ } else if (document.activeElement) {
+ document.activeElement.blur();
+ }
+ } else if (event.key === 'Enter' && this.onEnter) {
+ this.onEnter(event);
+ }
+ }
+
+ /**
+ * Get an array of focusable elements within the current containers.
+ * @returns {Element[]}
+ */
+ #getFocusable() {
+ const focusable = [];
+ const selector = '[tabindex]:not([tabindex="-1"]),[href],button:not([tabindex="-1"]),input:not([type=hidden])';
+ for (const container of this.containers) {
+ focusable.push(...container.querySelectorAll(selector))
+ }
+ return focusable;
+ }
+}
\ No newline at end of file