A concise JavaScript LRU cache.

lru.js

this.cache = (function() {
    // Inserts a node into a circular double linked list
    var insert = function(head, node) {
        return (((node.prev = head.prev).next = node).next = head).prev = node;
    };
    
    // Removes a node from a circular double linked list
    var remove = function(node) {
        return ((node.prev.next = node.next).prev = node.prev) && node;
    };
    
    return function(source, lines) {
        var index = {}, cache = (function() {
            this.next = this.prev = this;
        })();
        
        return function(key) {
            if(index.hasOwnProperty(key)) {
                cache = insert(cache, remove(index[key]));
            } else {
                cache = index[key] = insert(cache, {
                    key: key, value: source(key)
                });
                
                // Remove the oldest element if the cache is full
                lines - 1 ? lines -- : delete index[remove(cache.prev).key];
            }
            
            return cache;
        };
    };
})();