@signaldb/opfs

What is OPFS? The Origin Private File System (OPFS) is a private file system that browsers provide to each website (origin). Pages can create, read and write files in it without any permission prompt, and the files are invisible to the user and to other sites. OPFS is part of the File System API and is supported in all current major browsers (Chrome, Edge, Firefox and Safari).

Compared to other browser storage (see localStorage vs IndexedDB vs OPFS for details):

	localStorage	IndexedDB	OPFS
Data model	string key/value	object store with indexes	files and directories
API	synchronous	asynchronous (event-based)	asynchronous; fast synchronous access in Web Workers
Capacity	a few MB per origin	large (quota-based)	large (quota-based)
Typical use	small settings	structured app data	large files, databases, binary data

@signaldb/opfs stores the documents of a SignalDB collection as a folder in OPFS, with one file per document and one file per indexed value. This gives you persistent local storage for your data with a single line of configuration, which is useful for offline-first apps.

createOPFSAdapter (default)

import { Collection, DefaultDataAdapter } from '@signaldb/core'
import createOPFSAdapter from '@signaldb/opfs'

const dataAdapter = new DefaultDataAdapter({
  storage: name => createOPFSAdapter(name),
})

const Posts = new Collection('posts', dataAdapter)

Function to create a OPFS adapter for use with a collection. The OPFS Adapter is another way to store data in a browser environment. This adapter is based on the Origin Private File System API. It is a simple and straightforward way to store data in the browser's filesystem.

A data adapter asks its storage function for one adapter per collection and passes the collection's name, which is why the function above uses that name as the folder.

Parameters

• folderName - The folder this collection lives in, relative to the origin private file system root.
• options - (Optional) Configuration object with the following properties:
  • serialize - (Optional) Turns a stored value into a string. Default is JSON.stringify.
  • deserialize - (Optional) Reads that string back. Default is JSON.parse.

Like the Filesystem Adapter, the adapter is given a folder rather than a file: items/ holds one file per document, index/ one file per indexed value.

Requirements

The adapter needs navigator.storage.getDirectory() and FileSystemFileHandle#createWritable() for reading and writing files, and the Web Locks API (navigator.locks): every read and write of a file runs under an exclusive lock named after its path, so tabs and workers of the same origin never interleave a read with a write to the same file. All of these are only available in secure contexts (HTTPS or localhost); without them the adapter cannot access its files.

The OPFS Adapter is an alternative to the Filesystem Adapter. The OPFS Adapter can only be used in a browser environment, while the Filesystem Adapter can only be used in a Node.js environment.

Credits to jamesgibson14