lru-cache-idb

A least-recently-used (LRU) cache for web applications, based on IndexedDB.

Introduction

IndexedDB providing in-browser persistence for web applications is an obvious tool for use as a cache. On the other hand, using browser storage for caching leads to specific challenges, such as the fact that multiple instances of a web site (open in multiple tabs, for instance) all access the same storage.

Design:

• Batched updates: every read operation on an LRU cache leads to modifications in the stored data, and hence to a write operation. Since a cache may be read very often it is important to provide cheap reads, and hence to avoid writing to persistence on every invocation. In order to minimize the actual writes to IndexedDB, this library batches writes and only persists them periodically (default: every 15s). As a downside, this can lead to data loss if the application is closed in the meantime, or if the same page open in another tab evicts old data.
• Batched deletes: data eviction by default is also performed in batches running at most once per specified time interval, 1 minute by default. In the meantime, the cache may grow beyond its specified capacity.
• Memory layer: besides the data stored in IndexedDB it is possible to configure an additional memory cache, typically retaining a subset of cached items in memory.
• Dependency-free: no third-party Javascript libraries used.
• Modern Javascript: implemented in Typescript as an ESM module.

Demo: https://cnoelle.github.io/lru-cache-idb/

Getting started

Install: npm install lru-cache-idb

Basic usage:

import { createCacheIdb } from "lru-cache-idb";

const cache = createCacheIdb({maxItems: 1000, memoryConfig: {maxItemsInMemory: 100}});
await cache.set("entry1", {a: 1, description: "The first entry"});
await cache.set("entry2", {a: 2, description: "The 2nd entry"});
const obj = await cache.get("entry1");
console.log("Object found:", obj);

It is possible to instantiate multiple caches on one page, but the database names must differ:

const cache = createCacheIdb({database: "MySpecialDb", maxItems: 1000, memoryConfig: {maxItemsInMemory: 100}});

This is the database name in IndexedDB, the default being "LruIdbItemsCache". The existing databases/caches on a page can be viewed in the browser developer console, e.g. under Web Storage->Indexed DB (Firefox) or Application->Storage->IndexedDB (Chrome).

API documentation: https://cnoelle.github.io/lru-cache-idb/docs/index.html

Develop

After cloning the repository, install the dev dependencies: npm install.

Build

npm run build

Demo app

This repository contains a sample HTML file index.html using the library. For instance, start a dev server using npx http-server, then the page will be available in the browser at http://localhost:8080 (check port in console output). Build first, index.html refers to the compiled Javascript files in the dist/ folder. The demo app can also be found at https://cnoelle.github.io/lru-cache-idb/.

Tests

Tests run in NodeJS and hence cannot access an actual browser's IndexedDB implementation. Instead, they run against fake-indexeddb. To run all tests, build first, then:

npm run test

To run tests in a single file:

npx ava ./test/testDefaultCache.js

In order to run a single test in a single file, replace test("...", async t => { at the beginning of the test by test.only("...", async t => {.

Generate documentation

Documentation is generated using typedoc. Run

npm run docs

and find the updated documentation in the docs subfolder.