lru cache

cache.js

function Cache(max, ttl) {
    let items = {},
        size = 0,
        first = undefined,
        last = undefined;

    return $ = {
        has(key) {
            return key in items;
        },

        clear() {
            first = last = undefined;
            size = 0;
            items = {};
        },

        evict() {
            if (size > 0) {
                let item = last;
                delete items[item.key];
                size--;

                if (size === 0) first = last = undefined;
                else {
                    last = item.prev;
                    last.next = undefined;
                }
            }
        },
        
        delete(key) {
            let item;
            if (item = items[key]) {
                delete items[key];
                size--;

                if (item.next) item.next.prev = item.prev;
                if (item.prev) item.prev.next = item.next
                if (item === first) first = item.next;
                if (item === last) last = item.prev;
            }
        },

        get(key) {
            let item, value;

            if (item = items[key]) {
                if (ttl > 0 && item.expire <= new Date().getTime()) $.delete(key);
                else {
                  value = item.value;
                  $.set(key, value); // move item to front of list
                }
            }

            return value;
        },

        set(key, value) {
            let item = items[key];

            if (item) {
                if (item !== first) {
                    let n = item.next,
                        p = item.prev;

                    if (item === last) last = item.prev;

                    item.prev = undefined;
                    item.next = first;
                    first.prev = item;

                    if (p) p.next = n;
                    if (n) n.prev = p;
                }
            } else {
                if (size === max) $.evict();

                item = items[key] = {
                    expire: ttl > 0 ? new Date().getTime() + ttl : ttl,
                    key,
                    prev: undefined,
                    next: first,
                    value
                };

                if (++size === 1) last = item;
                else first.prev = item;
            }

            first = item;
        }
    };
};