function shouldIgnoreFocusHandling()

in src/focus-zone.ts [246:312]
45 lines of code
30 McCabe index (conditional complexity)

function shouldIgnoreFocusHandling(keyboardEvent: KeyboardEvent, activeElement: Element | null) {
  const key = keyboardEvent.key

  // Get the number of characters in `key`, accounting for double-wide UTF-16 chars. If keyLength
  // is 1, we can assume it's a "printable" character. Otherwise it's likely a control character.
  // One exception is the Tab key, which is technically printable, but browsers generally assign
  // its function to move focus rather than type a <TAB> character.
  const keyLength = [...key].length

  const isTextInput =
    (activeElement instanceof HTMLInputElement && activeElement.type === 'text') ||
    activeElement instanceof HTMLTextAreaElement

  // If we would normally type a character into an input, ignore
  // Also, Home and End keys should never affect focus when in a text input
  if (isTextInput && (keyLength === 1 || key === 'Home' || key === 'End')) {
    return true
  }

  // Some situations we want to ignore with <select> elements
  if (activeElement instanceof HTMLSelectElement) {
    // Regular typeable characters change the selection, so ignore those
    if (keyLength === 1) {
      return true
    }
    // On macOS, bare ArrowDown opens the select, so ignore that
    if (key === 'ArrowDown' && isMacOS() && !keyboardEvent.metaKey) {
      return true
    }
    // On other platforms, Alt+ArrowDown opens the select, so ignore that
    if (key === 'ArrowDown' && !isMacOS() && keyboardEvent.altKey) {
      return true
    }
  }

  // Ignore page up and page down for textareas
  if (activeElement instanceof HTMLTextAreaElement && (key === 'PageUp' || key === 'PageDown')) {
    return true
  }

  if (isTextInput) {
    const textInput = activeElement as HTMLInputElement | HTMLTextAreaElement
    const cursorAtStart = textInput.selectionStart === 0 && textInput.selectionEnd === 0
    const cursorAtEnd =
      textInput.selectionStart === textInput.value.length && textInput.selectionEnd === textInput.value.length

    // When in a text area or text input, only move focus left/right if at beginning/end of the field
    if (key === 'ArrowLeft' && !cursorAtStart) {
      return true
    }
    if (key === 'ArrowRight' && !cursorAtEnd) {
      return true
    }

    // When in a text area, only move focus up/down if at beginning/end of the field
    if (textInput instanceof HTMLTextAreaElement) {
      if (key === 'ArrowUp' && !cursorAtStart) {
        return true
      }
      if (key === 'ArrowDown' && !cursorAtEnd) {
        return true
      }
    }
  }

  return false
}