JQUERY - Speeding Up Code

I have a generic question. I've heard many times that a great way to speed up your code is to not call the same selector over and over again - eg - 4 times one DIV selector:

    if($('div#spotJoinSite').is(':visible')) {
        var pos = $('div#spotJoinSite').offset();  
        var width = $('div#spotJoinSite').width();
        var height = $('div#spotJoinSite').height();
        $('div#container_join_messages').css({'position': 'fixed'});        
    }

Would it therefore be a good idea to have a section at the top of a js script that connected all the required selectors to variables - eg:

        var spotJoinSite = $('div#spotJoinSite');
        var container_join_messages = $('div#container_join_messages');

The the variables could be exclusively used.

Is this a good idea or a bad idea? What speed increases could be expected? noticable or not? What are the potential problems?开发者_Go百科 Would you do it?

If the variable names are same as the selector it would be easy to reference them.

---

Yes, it is proabably noticeable on slow computers or on very hard applications like minigames in jQuery/javascript