y-localstorage

a simple Yjs storage provider persisting in localStorage (for educational purposes only!)

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.

This module implements a simple Yjs storage provider for browser-based applications which uses localStorage for persistance. In addition to other database providers it

• contains an isSynced property which reflects the main document's current synchronization status,
• emits additional events (sync-started, sync-continued, sync-finished and sync-aborted) which inform about synchronization progress for the main document,
• recognizes subdocs (which will then automatically be persisted 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-localstorage 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)

Nota bene: do not use this provider in production - it has solely be written for educational purposes!

Installation

y-localstorage 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-localstorage

or load the plain script file directly

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

Access

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

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

Alternatively, you may access the global variable LocalStorageProvider 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 { LocalStorageProvider } from 'y-localstorage'
</script>

<script>
  const sharedDoc   = new Y.Doc()
  const Persistence = new LocalStorageProvider('local-persistence', 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:

  ...
  const Persistence = new LocalStorageProvider('local-persistence', sharedDoc)
  ...

API Reference

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

Constructor

• LocalStorageProvider (DocName:string, sharedDoc:Y.Doc, CounterLimit:number = 5)creates a new instance of LocalStorageProvider which synchronizes the given sharedDoc on localStorage. DocName is used as a prefix for the keys under which updates of sharedDoc are stored. CounterLimit indicates how many updates will just be appended to localStorage before they will be compacted into a single one

Properties

• isSyncedreturns true while the initially given Y.Doc and this provider are in-sync - or false otherwise

Events

• on('sync-started', Handler:(Provider:LocalStorageProvider, 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:LocalStorageProvider, 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:LocalStorageProvider, 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:LocalStorageProvider, 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:LocalStorageProvider) => voidthe 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

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