@cachemap/indexed-db

The Cachemap IndexedDB module.


Keywords
cachemap, cache, IndexedDB, isomorphic, localstorage, redis
License
MIT
Install
npm install @cachemap/indexed-db@4.0.0

Documentation

cachemap

An extensible, isomorphic cache with modules to interface with Redis, LocalStorage, IndexedDB and an in-memory Map.

build-and-deploy License: MIT

Summary

  • Use Redis or an in-memory Map on the server.
  • Use LocalStorage, IndexedDB or an in-memory Map on the client.
  • Extend with custom modules to interface with key/value databases of your choosing.
  • Transfer entries from one Cachemap to another.
  • Store entries alongside cache-control directives, etags and uuids.
  • Cache-control directives used to derive whether entries are fresh or stale.
  • Prioritize entries based on metadata stored against each entry.
  • Use a reaper to cull stale entries at specified intervals.
  • Set maximum memory size for total entries.
  • Use on browser's main or worker thread.

Installation

Cachemap is structured as a monorepo, so each package is published to npm under the @cachemap scope and can be installed in a project in the same way as any other npm package.

yarn add @cachemap/<package>

So, for example, if you want a server cache that uses Redis you would install the packages below.

yarn add @cachemap/core @cachemap/redis

If, however, you want a persisted client cache that uses IndexedDB and culls stale data you would install the following packages.

yarn add @cachemap/core @cachemap/indexed-db @cachemap/reaper

Packages

The Cachemap's multi-package structure allows you to compose your cache of the modules you need, without additional bloat. Start with the @cachemap/core package and build out from there.

Usage

The Cachemap API is similar to that of a Map, it has clear, delete, entries, get, has and set methods, as well as Cachemap specific import, export and size methods. Each module that interfaces with a database, referred to as a store, also has these methods. The API provides a simple and consistent way to communicate with key/value databases.

Creating a Cachemap instance

The Cachemap is initialized using the traditional class constructor. Any modules you want to add to the Cachemap, like the store to work with your database or the reaper to prune stale entries, are passed as properties to the constructor.

The default export of each module is a curried function that returns an async function that initializes the module. This allows you and the Cachemap to pass configuration options into the module.

import Cachemap from "@cachemap/core";
import indexedDB from "@cachemap/indexed-db";
import reaper from "@cachemap/reaper";

const cachemap = new Cachemap({
  name: "foobar",
  reaper: reaper({ interval: 300000 }),
  store: indexedDB(),
  type: "someType",
});

The example above initializes a persisted cache for the browser that uses IndexedDB as its database and checks for stale entries every five minutes. No other configuration is required, as long as the browser supports IndexedDB you are good to go. For a full list of configuration options, see the @cachemap/core documentation.

Checking, getting, setting, deleting

The bread and butter of the Cachemap's functionality are the delete, get, has, and set methods. The input signatures of the first three are very similar, each excepts a key as the first argument and a set of options as the second. The set method, meanwhile, excepts a key as the first argument, a value as the second and the third is the options.

An important set option is cacheHeaders. This takes a Headers instance or a plain object of HTTP headers. The etag and cache-control directives are filtered out and stored against an entry. The directives are used to generate a TTL (time to live) that the Cachemap checks whenever accessing the entry.

Another important set option is tag. This allows you to store an arbitrary identifier against an entry, like a request or session ID. These identifiers can come in handy, for example, if you want to export all entries added during a particular request.

All four methods have a hash option that runs the key through md5 to create a short unique string, which can be useful if the original keys are long strings such as URLs or GraphQL queries.

(async () => {
  const key = "https://api.example.com/user/foobar";
  const value = { email: "foobar@example.com", id: "12345", name: "foobar" };
  const cacheHeaders = { cacheControl: "private, max-age=60" };

  await cachemap.set(key, value, { cacheHeaders, hash: true });
  // returns undefined

  const cacheability = await cachemap.has(key, { hash: true });
  // returns an instance of the Cacheability module, which includes the
  // cache-control directives and the TTL calculated from the directives

  const entry = await cachemap.get(key, { hash: true });
  // returns { email: "foobar@example.com", id: "12345", name: "foobar" }

  const deleted = await cachemap.delete(key, { hash: true });
  // returns true
})();

For full details of each method's signature, see the @cachemap/core documentation.

Bulk operations

Sometimes you might want to add or retrieve multiple entries at once, and this is where the import and export methods come in. They allow you to bulk transfer entries and their metadata between two Cachemaps. You can export all entries or a subset based on specific keys or a particular tag.

This could be used to pass entries between a Cachemap on the server and one on the browser. The server Cachemap could, for example, export all entries and metadata added during a request to the server, then this could be serialized and embedded in the response body, from where it could be imported into the browser Cachemap.

(async () => {
  const requestID = "6d91e84e-b14c-11e8-96f8-529269fb1459";

  const entries = await cachemapOne.export({ tag: requestID });
  // returns { entries: Array<[string, any]>, metadata: Array<{ [key: string]: any }> }

  await cachemapTwo.import(entries);
  // returns undefined
})();

For full details of each method's signature, see the @cachemap/core documentation.

Web worker

To free up the browser's main thread you can run the Cachemap in a web worker. For this you need the @cachemap/core-worker package in addition to @cachemap/core, a store and optional reaper package.

The package exports the CoreWorker class that you initialize on the main thread and the registerWorker method to use in your worker.js file. The CoreWorker class method signatures are identical to those of the Core class.

// main.js

import CachemapWorker from "@cachemap/core-worker";

const cachemap = new CachemapWorker({
  name: "integration-tests",
  worker: new Worker("worker.js"),
  type: "someType",
});
// worker.js

import Cachemap from "@cachemap/core";
import { registerWorker } from "@cachemap/core-worker";
import indexedDB from "@cachemap/indexed-db";
import reaper from "@cachemap/reaper";

const cachemap = new Cachemap({
  name: "worker-integration-tests",
  reaper: reaper({ interval: 300000 }),
  store: indexedDB(),
  type: "someType",
});

registerWorker({ cachemap });

The example above initializes a persisted browser cache that runs on the worker thread and uses the IndexedDB and reaper modules. For a full list of configuration options, see the @cachemap/core-worker documentation.

Controlling multiple instances

Sometimes you'll want to control multiple Cachemap instances that are not directly accessible. You can do this through the @cachemap/controller package. The package exports an eventemitter-based module that has methods for clearing instances caches and starting/stopping each instance's reaper module.

Each Cachemap instance is listening for these events and will action them if the name or type props passed into the method match the instance's.

import controller from "@cachewmap/controller";

controller.clearCaches({ type: "someType" });
controller.stopReapers({ type: "someType" });

Custom modules

The Cachemap comes with four store modules, but you can create additional stores to work with key/value databases of your choosing. A store just has to adhere to the structure below. If you are writing in Typescript, you can even import the Store interface from @cachemap/core and have your store class implement that.

// store class must implement this interface
interface Store {
  readonly maxHeapSize: number;
  readonly name: string;
  readonly type: string;
  clear(): Promise<void>;
  delete(key: string): Promise<boolean>;
  entries(keys?: string[]): Promise<Array<[string, any]>>;
  get(key: string): Promise<any>;
  has(key: string): Promise<boolean>;
  import(entries: Array<[string, any]>): Promise<void>;
  set(key: string, value: any): Promise<void>;
  size(): Promise<number>;
}

// async function must return store instance
type StoreInit = (options: { name: string }) => Promise<Store>;

Changelog

Check out the features, fixes and more that go into each major, minor and patch version.

License

Cachemap is MIT Licensed.