feat(SW-184): language switcher mobile/desktop functionality

utils/tabbable.ts

@@ -0,0 +1,62 @@
+/*!
+ * Adapted from jQuery UI core
+ *
+ * http://jqueryui.com
+ *
+ * Copyright 2014 jQuery Foundation and other contributors
+ * Released under the MIT license.
+ * http://jquery.org/license
+ *
+ * http://api.jqueryui.com/category/ui-core/
+ */
+
+const tabbableNode = /input|select|textarea|button|object/
+
+function hidesContents(element: HTMLElement) {
+  const zeroSize = element.offsetWidth <= 0 && element.offsetHeight <= 0
+
+  // If the node is empty, this is good enough
+  if (zeroSize && !element.innerHTML) return true
+
+  // Otherwise we need to check some styles
+  const style = window.getComputedStyle(element)
+  return zeroSize
+    ? style.getPropertyValue("overflow") !== "visible"
+    : style.getPropertyValue("display") === "none"
+}
+
+function visible(element: any) {
+  let parentElement = element
+  while (parentElement) {
+    if (parentElement === document.body) break
+    if (hidesContents(parentElement)) return false
+    parentElement = parentElement.parentNode
+  }
+  return true
+}
+
+export function focusable(element: HTMLElement, isTabIndexNotNaN: boolean) {
+  const nodeName = element.nodeName.toLowerCase()
+  const res =
+    //@ts-ignore
+    (tabbableNode.test(nodeName) && !element.disabled) ||
+    //@ts-ignore
+    (nodeName === "a" ? element.href || isTabIndexNotNaN : isTabIndexNotNaN)
+  return res && visible(element)
+}
+
+export function tabbable(element: HTMLElement) {
+  let tabIndex = element.getAttribute("tabindex")
+  //@ts-ignore
+  if (tabIndex === null) tabIndex = undefined
+  //@ts-ignore
+  const isTabIndexNaN = isNaN(tabIndex)
+  //@ts-ignore
+  return (isTabIndexNaN || tabIndex >= 0) && focusable(element, !isTabIndexNaN)
+}
+
+export default function findTabbableDescendants(
+  element: HTMLElement
+): HTMLElement[] {
+  return [].slice.call(element.querySelectorAll("*"), 0).filter(tabbable)
+}