trap focus

trap_focus.js.coffee

# based of https://accessibility.oit.ncsu.edu/blog/2015/02/13/the-incredible-accessible-modal-window-version-3/
class FocusTrap
  @init = (evt, $domNode) ->
    focusableElements = 'a[href], button, input:not([disabled]), select:not([disabled]), textarea, *[contenteditable]'

    if evt.which == 9
      o = $domNode.find('*')
      focusableItems = o.filter(focusableElements).filter(':visible')
      return unless focusableItems.length

      focusedItem = jQuery(':focus')
      numberOfFocusableItems = focusableItems.length
      focusedItemIndex = focusableItems.index(focusedItem)

      if evt.shiftKey
        if focusedItemIndex == 0
          focusableItems.get(numberOfFocusableItems - 1).focus()
          evt.preventDefault()
      else if (focusedItemIndex == numberOfFocusableItems - 1) || focusedItemIndex == -1
        focusableItems.get(0).focus()
        evt.preventDefault()