When you add a custom JavaScript code in a Layout CSS/JS field it affect BB edit mode as well. But not always you want the function when you editing a page. This snippet ( typeof FLBuilder != 'undefined' ) will deactivate the function.

(function ($) {

  $(document).ready(function() {
    if ( typeof FLBuilder != 'undefined' ) {//deactivate on BB edit mode
      return;
    }else{

      //Do your magic here
      $("button").click(function(){
        $("p").hide();
      });

    }
  });

})(jQuery);