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y-localforage

a simple Yjs storage provider using localForage for persistence

Yjs provides a complete ecosystem for (persisting and) sharing "Conflict-free replicated data types" (CRDT) among multiple clients using a variety of persistence and communication providers. LocalForage is a simple storage library for JavaScript which wraps IndexedDB, WebSQL and other storage technologies in a common, localStorage-like API.

This module implements a simple Yjs storage provider for browser-based applications which uses an arbitrary localForage store for persistance - this means: if there is a localForage "driver" for a storage of your choice, you can use this module to immediately instantiate a Yjs provider for it.

In addition to other database providers y-localforage

  • contains an isSynced property which reflects the main document's own current synchronization status,
  • and an isFullySynced property which includes the synchronization state of any subdocs,
  • emits additional events (sync-started, sync-continued, sync-finished and sync-aborted) which inform about synchronization progress for the main document,
  • and subdoc-synced which informs about a given subdoc being successfully synchronized,
  • sends a load event to the main doc and any subdoc as soon as that Y.Doc has been fully loaded from persistence,
  • automatically persists any subdocs as well, and
  • includes rudimentary error handling which breaks down the provider upon failure (which means that you have to re-incarnate the provider after the cause for this failure has been removed).

y-localforage always tries to keep your data safe and not to overwrite or even delete previously written updates. Even a failure normally only means that the last update could not be written but all the previous ones are still safe.

Important: do not use the "copy" feature for Y.Docs, i.e., do not create a Y.Doc instance with the same GUID as another one - Y.Doc copies do not "synchronize" as described in the docs anyway.

NPM users: please consider the Github README for the latest description of this package (as updating the docs would otherwise always require a new NPM package version)

Just a small note: if you like this work and plan to use it, consider "starring" this repository (you will find the "Star" button on the top right of this page), so that I know which of my repositories to take most care of.

Installation

y-localforage may be used as an ECMAScript module (ESM), a CommonJS or AMD module or from a global variable.

You may either install the package into your build environment using NPM with the command

npm install y-localforage localforage

or load the plain script files directly

<script src="https://unpkg.com/localforage"></script>
<script src="https://unpkg.com/y-localforage"></script>

Access

How to access the package depends on the type of module you prefer

  • ESM (or Svelte): import { LocalForageProvider } from 'y-localforage'
  • CommonJS: const LocalForageProvider = require('y-localforage')
  • AMD: require(['y-localforage'], (LocalForageProvider) => {...})

Alternatively, you may access the global variable LocalForageProvider directly.

Note for ECMAScript module users: all module functions and values are exported individually, thus allowing your bundler to perform some "tree-shaking" in order to include actually used functions or values (together with their dependencies) only.

Usage within Svelte

For Svelte, it is recommended to import the package in a module context. From then on, its exports may be used as usual:

<script context="module">
  import * as Y from 'yjs'
  import { LocalForageProvider } from 'y-localforage'
</script>

<script>
  localforage.config({
    driver: [localforage.INDEXEDDB, localforage.WEBSQL]
  })

  localforage.ready(function () {
    const DocStore = localforage.createInstance({
      name:'Yjs-Persistence'
    })

    const sharedDoc   = new Y.Doc()
    const Persistence = new LocalForageProvider(DocStore, sharedDoc)
    ...
  })
</script>

Usage as ECMAscript, CommonJS or AMD Module (or as a global Variable)

Let's assume that you already "required" or "imported" (or simply loaded) the module according to your local environment. In that case, you may use it as follows:

  ...
  localforage.config({
    driver: [localforage.INDEXEDDB, localforage.WEBSQL]
  })

  localforage.ready(function () {
    const DocStore = localforage.createInstance({
      name:'Yjs-Persistence'
    })

    const sharedDoc   = new Y.Doc()
    const Persistence = new LocalForageProvider(DocStore, sharedDoc)
    ...
  })

API Reference

The following documentation shows method signatures as used by TypeScript - if you prefer plain JavaScript, just ignore the type annotations.

Constructor

  • LocalForageProvider (Store:any, sharedDoc:Y.Doc, UpdateLimit:number = 500)
    creates a new instance of LocalForageProvider which synchronizes the given sharedDoc on the given localForage Store. UpdateLimit indicates how many updates should be appended to the Store before they will be compacted into a single one

Properties

  • isSynced
    returns true while the initially given Y.Doc and this provider are in-sync - or false otherwise. Please note, that isSynced does not inform about the synchronization status of any "subdocs"
  • isFullySynced
    returns true while the initially given Y.Doc and all its "subdocs" are in-sync - or false otherwise

Methods

  • SubDocIsSynced (SubDoc:Y.Doc):boolean
    returns true while the given SubDoc (of this provider's shared Y.Doc) and its provider are in-sync - or false otherwise. SubDocIsSynced also returns false if SubDoc is not a subdoc of this provider's shared Y.Doc
  • async destroy ():Promise<void>
    stops any activities of this provider and deletes any persistence entries of this provider's shared Y.Doc and its subdocs. Warning: this method completely destroys any written data and cannot be undone!

Events

  • on('sync-started', Handler:(Provider:LocalForageProvider, Progress:number) => void)
    the sync-started event is fired whenever a synchronization between this provider and its associated Y.Doc has begun. Provider contains a reference to this provider and Progress is always 0.0
  • on('sync-continued', Handler:(Provider:LocalForageProvider, Progress:number) => void)
    the sync-continued event may be fired several times while a synchronization between this provider and its associated Y.Doc is in progress if this synchronization can not be completed instantaneously. Provider contains a reference to this provider and Progress is a number between 0.0 and 1.0 indicating how much has already been synchronized. Please note: depending on how many new updates are generated (in contrast to how many have been synchronized during that time) the reported Progress may not always increase but may even decrease sometimes
  • on('sync-finished', Handler:(Provider:LocalForageProvider, Progress:number) => void)
    the sync-finished event is fired whenever a synchronization between this provider and its associated Y.Doc has finished. Provider contains a reference to this provider and Progress is always 1.0
  • on('sync-aborted', Handler:(Provider:LocalForageProvider, Progress:number) => void)
    the sync-aborted event is fired when a synchronization between this provider and its associated Y.Doc has been aborted (e.g., because the space on localStorage was exhausted or the provider was destroyed). Provider contains a reference to this provider and Progress is always 1.0. After such an event, the Provider remains unusable and has to be created again
  • on('synced', Handler:(Provider:LocalForageProvider) => void
    the synced event works like in any other Yjs provider and is fired whenever (initially or after an update to the associated Y.Doc) this provider gets in-sync again
  • on('subdoc-synced', Handler:(Provider:LocalForageProvider, SubDoc:Y.Doc) => void
    the subdoc-synced event is fired whenever any "subdoc" of this provider's main Y.Doc has been successfully synchronized. Provider contains a reference to this provider and SubDoc a reference to the synchronized subdoc

Build Instructions

You may easily build this package yourself.

Just install NPM according to the instructions for your platform and follow these steps:

  1. either clone this repository using git or download a ZIP archive with its contents to your disk and unpack it there
  2. open a shell and navigate to the root directory of this repository
  3. run npm install in order to install the complete build environment
  4. execute npm run build to create a new build

You may also look into the author's build-configuration-study for a general description of his build environment.

License

MIT License