code: function bindFocusables( instance, activateOnFocus ) {
    if ( document.querySelectorAll ) {
      try {
        const node = ReactDOM.findDOMNode( instance );
        if ( node ) {
          const focusables = node.querySelectorAll( focusableSelector );
          if ( focusables.length ) {
            const onFocus = element => {
              const onFocusPrev = element.onfocus;
              return function( event ) {
                activateOnFocus( instance );
                if ( onFocusPrev ) onFocusPrev.call( element, event );
              };
            };
            Array.prototype.slice.call( focusables ).forEach( element => (
              element.onfocus = onFocus( element )
            ) );
          }
        }
      } catch ( error ) {
        // noop, mostly suppressing error here https://github.com/glortho/react-keydown/issues/76
      }
    }
  }
docs: bindFocusables: Find any focusable child elements of the component instance and
  add an onFocus handler to focus our keydown handlers on the parent component
  when user keys applies focus to the element.
  
  NOTE: One limitation of this right now is that if you tab out of the
  component, _focusedInstance will still be set until next click or mount or
  controlled focus.
  
  @access public
  @param {object} instance The key-bound component instance
  @param {callback} activateOnFocus The fn to fire when element is focused