jQuery caching

Simple but smart. I love it.

I particularly like that you don't have the overhead of pre-caching your selectors in separate variables at the top of your method, namespace, or constructor. Have you tried this in a project with Backbone? I typically cache my elements as properties of my View instances: myNavView.$nav = $('#nav'). That could simply become $$('#nav'), no?

Good if your DOM don't change between two calls.

Here's a modified version that hides the cache variable inside a closure:

var $$ = (function() {
    var cache = {};
    return (function (selector) {
        return cache[selector] || ( cache[selector] = jQuery (selector) );
    });
})();

@mlb You have a point - this pattern is problematic with dynamic websites. But you could implement some cache invalidation for that.