memory-cache-node

A fast and type safe memory cache for Node.js and browser. memory-cache-node use Javascript Map as cache implementation which is faster than using Javascript object that some other similar libraries use. memory-cache-node also uses implementation that does not block the event loop for a long time, if the cache is very large (hundreds of thousands or millions of entries).

Table of Contents

• Installation
• Usage
• API Documentation
• License

Installation

npm install --save memory-cache-node

Usage

Creating a memory cache

Below example creates a memory cache for items which has string keys and number values. Memory cache checks expiring items every 600 seconds (i.e. every 10 minutes) The maximum number of items in the cache is 1 million.

import { MemoryCache } from 'memory-cache-node';

const itemsExpirationCheckIntervalInSecs = 10 * 60;
const maxItemCount = 1000000;
const memoryCache = new MemoryCache<string, number>(itemsExpirationCheckIntervalInSecs, maxItemCount);

Storing items in the memory cache

Below example stores a permanent item in the memory cache with key key1 and stores an expiring item with key key2. The latter item expires earliest after 30 minutes.

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
memoryCache.storePermanentItem('key1', 1);

const timeToLiveInSecs = 30 * 60;
memoryCache.storeExpiringItem('key2', 2, timeToLiveInSecs);

Getting the number of items in the memory cache

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
memoryCache.storePermanentItem('key1', 1);

const timeToLiveInSecs = 30 * 60;
memoryCache.storeExpiringItem('key2', 2, timeToLiveInSecs);
console.log(memoryCache.getItemCount()); // Logs to console: 2

Checking if an item exists in the memory cache

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
memoryCache.storePermanentItem('key1', 1);

console.log(memoryCache.hasItem('key1')); // Logs to console: true
console.log(memoryCache.hasItem('notFound')); // Logs to console: false

Retrieving the value of an item in the memory cache

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
memoryCache.storePermanentItem('key1', 1);

console.log(memoryCache.retrieveItemValue('key1')); // Logs to console: 1
console.log(memoryCache.retrieveItemValue('notFound')); // Logs to console: undefined

Changing the item expiration timestamp

You can set the item expiration time for both permanent and already expiring items.

To an absolute expiration time

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
memoryCache.storeExpiringItem('key1', 1, 60);

// Expire at the end of this year, instead of in 60 seconds:
const endOfThisYear = new Date(new Date().getFullYear(), 11, 31);
memoryCache.setItemTimeToLiveUntil('key1', endOfThisYear.getTime());

With a relative expiration time

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
memoryCache.storePermanentItem('key1', 1);

memoryCache.setItemTimeToLiveRemaining('key1', 5); // expire in 5 seconds from now instead of never

Making an expiring item permanent

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
memoryCache.storeExpiringItem('key1', 1, 60);

memoryCache.setItemTimeToLiveUntil('key1', undefined); // Never expire

Getting the item expiration timestamp

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
memoryCache.storePermanentItem('key1', 1);

console.log(memoryCache.getItemExpirationTimestampInMillisSinceEpoch('key1')); // Logs some large number to console

Removing an item from the memory cache

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
memoryCache.storePermanentItem('key1', 1);
console.log(memoryCache.hasItem('key1')); // Logs to console: true
memoryCache.removeItem('key1');
console.log(memoryCache.hasItem('key1')); // Logs to console: false

Clearing the memory cache

Below examples removes all items from the memory cache

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
// Use cache here
// ...
memoryCache.clear()

Destroying the memory cache

Below example destroys the memory cache and it should not be used after that. It clears the memory cache and also removes the timer for checking expired items. NOTE! You should NEVER use a destroyed cache again! If you try to use a destroyed memory cache, an exception will be thrown. You should destroy your memory cache if it is not used in your application anymore.

import { MemoryCache } from 'memory-cache-node';

const memoryCache = new MemoryCache<string, number>(600, 1000000);
// Use cache here
// ...
memoryCache.destroy()

API Documentation

• K is the type of the item key.
• V is the type of the item value.

class MemoryCache<K, V> {
  constructor(itemsExpirationCheckIntervalInSecs: number, maxItemCount: number);
  storePermanentItem(itemKey: K, itemValue: V): void;
  storeExpiringItem(itemKey: K, itemValue: V, timeToLiveInSecs: number): void;
  getItemCount(): number;
  hasItem(itemKey: K): boolean;
  getValues(): V[];
  getItems(): [K, V][];
  retrieveItemValue(itemKey: K): V | undefined;
  setItemTimeToLiveUntil(itemKey: K, timeToLiveUntilInMillisSinceEpoch: number | undefined): void;
  setItemTimeToLiveRemaining(itemKey: K, timeToLiveInSecs: number | undefined): void;
  getItemExpirationTimestampInMillisSinceEpoch(itemKey: K): number | undefined;
  removeItem(itemKey: K): void;
  exportItemsToJson(): string;
  
  // Use below function only with JSON output from exportItemsToJson method
  importItemsFrom(json: string): void; // Can throw if JSON is invalid
  
  clear(): void;
  destroy(): void;
}

License

MIT