function ensureTrapZoneHasFocus()

in src/focus-trap.ts [72:108]
26 lines of code
11 McCabe index (conditional complexity)

  function ensureTrapZoneHasFocus(focusedElement: EventTarget | null) {
    if (focusedElement instanceof HTMLElement && document.contains(container)) {
      if (container.contains(focusedElement)) {
        // If a child of the trap zone was focused, remember it
        lastFocusedChild = focusedElement
        return
      } else {
        if (lastFocusedChild && isTabbable(lastFocusedChild) && container.contains(lastFocusedChild)) {
          lastFocusedChild.focus()
          return
        } else if (initialFocus && container.contains(initialFocus)) {
          initialFocus.focus()
          return
        } else {
          // Ensure the container is focusable:
          // - Either the container already has a `tabIndex`
          // - Or provide a temporary `tabIndex`
          const containerNeedsTemporaryTabIndex = container.getAttribute('tabindex') === null
          if (containerNeedsTemporaryTabIndex) {
            container.setAttribute('tabindex', '-1')
          }
          // Focus the container.
          container.focus()
          // If a temporary `tabIndex` was provided, remove it.
          if (containerNeedsTemporaryTabIndex) {
            // Once focus has moved from the container to a child within the FocusTrap,
            // the container can be made un-refocusable by removing `tabIndex`.
            container.addEventListener('blur', () => container.removeAttribute('tabindex'), {once: true})
            // NB: If `tabIndex` was removed *before* `blur`, then certain browsers (e.g. Chrome)
            // would consider `body` the `activeElement`, and as a result, keyboard navigation
            // between children would break, since `body` is outside the `FocusTrap`.
          }
          return
        }
      }
    }
  }