LRU cache

Cache.js

var Cache = function(pMaxSize) {
    this.lastID = 0;
    this.items = {};
    this.numItems = 0;
    var maxSize = parseInt(pMaxSize, 10);
    if (isNaN(maxSize)) maxSize = -1;
    this.maxNumItems = maxSize;
    this.itemDefault = {
        ttl : 3600, // time to live = 1 hour
        priority : 2 // 1=low, 2=medium, 3=high
    };
};

Cache.prototype = {

    add : function(pKey, pValue, pTtl, pPriority) {
        if (!pKey || !pValue) return false;
        var ttl = pTtl || this.itemDefault.ttl, priority = pPriority || this.itemDefault.priority;
        if (this.items[pKey] !== null) {
            this.lastID++;
            this.del(pKey);
            this.items[pKey] = {
                id : this.lastID,
                key : pKey,
                value : pValue,
                ttl : ttl * 1000,
                priority : priority,
                accessed : new Date().getTime()
            };
        }
        if (this.maxNumItems > 0 && this.numItems >= this.maxNumItems) this.purge();
        this.numItems += 1;
        return this.items[pKey];
    },

    get : function(pKey) {
        var item = this.items[pKey];
        var get = null;
        if (item) {
            if (!this.isExpired(item)) {
                item.accessed = new Date().getTime();
                get = item.value;
            }
            else {
                this.del(pKey);
            }
        }
        return get;
    },

    del : function(pKey) {
        if (!pKey) return false;
        if (this.items[pKey]) {
            delete this.items[pKey];
            this.numItems -= 1;
            return true;
        }
        return false;
    },

    clear : function() {
        for ( var key in this.items) this.del(key);
        return true;
    },

    purge : function() {
        var cacheSize = this.numItems, itemsToKeep = [], item, lastItem;
        for ( var key in this.items) {
            item = this.items[key];
            if (this.isExpired(item)) {
                this.del(key);
            }
            else {
                itemsToKeep.push(item);
            }
        }
        if (itemsToKeep.length > this.maxNumItems) {
            // sort by priority and last accessed time
            itemsToKeep = itemsToKeep.sort(function(pItemA, pItemB) {
                // lower priority expires first
                if (pItemA.priority != pItemB.priority) {
                    return pItemB.priority - pItemA.priority;
                }
                // least recently accessed is less important,
                // it expires first
                if (pItemA.accessed != pItemB.accessed) {
                    return pItemB.accessed - pItemA.accessed;
                }
                // earliest created expires first
                return pItemB.id - pItemA.id;
            });
            // remove excess
            while (itemsToKeep.length > this.maxNumItems) {
                lastItem = itemsToKeep.pop();
                this.del(lastItem.key);
            }
        }
        return (this.numItems - cacheSize);
    },

    isExpired : function(pItem) {
        var now = new Date().getTime();
        return (pItem.ttl < (now - pItem.accessed));
    }

};