caching.js

function Selector_Cache() {
    var collection = {};
    function get_from_cache( selector ) {
        if ( undefined === collection[ selector ] ) {
            collection[ selector ] = $( selector );
        }
        return collection[ selector ];
    }
    return { get: get_from_cache };
}

var selectors = new Selector_Cache();

// Usage $( '#element' ) becomes
selectors.get( '#element' );