PowerSync SDK on NPM
This SDK is distributed via NPM [External link].
Source Code
Refer to packages/web in the powersync-js repo on GitHub.
API Reference
Full API reference for the PowerSync SDK [External link].
Example Projects
Gallery of example projects/demo apps built with JavaScript Web stacks and PowerSync.
Quickstart
📂 GitHub Repo https://github.com/powersync-community/vite-react-ts-powersync-supabase/SDK Features
- Real-time streaming of database changes: Changes made by one user are instantly streamed to all other users with access to that data. This keeps clients automatically in sync without manual polling or refresh logic.
- Direct access to a local SQLite database: Data is stored locally, so apps can read and write instantly without network calls. This enables offline support and faster user interactions.
- Asynchronous background execution: The SDK performs database operations in the background to avoid blocking the application’s main thread. This means that apps stay responsive, even during heavy data activity.
- Query subscriptions for live updates: The SDK supports query subscriptions that automatically push real-time updates to client applications as data changes, keeping your UI reactive and up to date.
- Automatic schema management: PowerSync syncs schemaless data and applies a client-defined schema using SQLite views. This architecture means that PowerSync SDKs can handle schema changes gracefully without requiring explicit migrations on the client-side.
Installation
Add the PowerSync Web NPM package to your project:@journeyapps/wa-sqlite
as a peer dependency. Install it in your app with:
By default, this SDK connects to a PowerSync instance via WebSocket (from
@powersync/web@1.6.0
) or HTTP streaming (before @powersync/web@1.6.0
). See Developer Notes for more details on connection methods.Getting Started
Before implementing the PowerSync SDK in your project, make sure you have completed these steps:- Signed up for a PowerSync Cloud account (here) or self-host PowerSync.
- Configured your backend database and connected it to your PowerSync instance.
- Installed the PowerSync Web SDK.
1. Define the Schema
The first step is defining the schema for the local SQLite database. This schema represents a “view” of the downloaded data. No migrations are required — the schema is applied directly when the local PowerSync database is constructed (as we’ll show in the next step).
The types available are
text
, integer
and real
. These should map directly to the values produced by the Sync Rules. If a value doesn’t match, it is cast automatically. For details on how Postgres types are mapped to the types below, see the section on Types in the Sync Rules documentation.
Example:
Note: No need to declare a primary key
id
column, as PowerSync will automatically create this.2. Instantiate the PowerSync Database
Next, you need to instantiate the PowerSync database — this is the core managed database. Its primary functions are to record all changes in the local database, whether online or offline. In addition, it automatically uploads changes to your app backend when connected. Example:SDK versions lower than 1.2.0In SDK versions lower than 1.2.0, you will need to use the deprecated WASQLitePowerSyncDatabaseOpenFactory syntax to instantiate the database.
3. Integrate with your Backend
The PowerSync backend connector provides the connection between your application backend and the PowerSync client-slide managed SQLite database. It is used to:- Retrieve an auth token to connect to the PowerSync instance.
- Apply local changes on your backend application server (and from there, to your backend database)
- PowerSyncBackendConnector.fetchCredentials - This is called every couple of minutes and is used to obtain credentials for your app backend API. -> See Authentication Setup for instructions on how the credentials should be generated.
- PowerSyncBackendConnector.uploadData - Use this to upload client-side changes to your app backend. -> See Writing Client Changes for considerations on the app backend implementation.
Using PowerSync: CRUD functions
Once the PowerSync instance is configured you can start using the SQLite DB functions. The most commonly used CRUD functions to interact with your SQLite data are:- PowerSyncDatabase.get - get (SELECT) a single row from a table.
- PowerSyncDatabase.getAll - get (SELECT) a set of rows from a table.
- PowerSyncDatabase.watch - execute a read query every time source tables are modified.
- PowerSyncDatabase.execute - execute a write (INSERT/UPDATE/DELETE) query.
Fetching a Single Item
The get method executes a read-only (SELECT) query and returns a single result. It throws an exception if no result is found. Use getOptional to return a single optional result (returnsnull
if no result is found).
Querying Items (PowerSync.getAll)
The getAll method returns a set of rows from a table.Watching Queries (PowerSync.watch)
The watch method executes a read query whenever a change to a dependent table is made.Mutations (PowerSync.execute, PowerSync.writeTransaction)
The execute method can be used for executing single SQLite write statements.Configure Logging
Enable verbose output in the developer tools for detailed logs.
Additional Usage Examples
See Usage Examples for further examples of the SDK.Developer Notes
Connection Methods
This SDK supports two methods for streaming sync commands:- WebSocket (Default)
- The implementation leverages RSocket for handling reactive socket streams.
- Back-pressure is effectively managed through client-controlled command requests.
- Sync commands are transmitted efficiently as BSON (binary) documents.
- This method is recommended since it will support the future BLOB column support feature.
- HTTP Streaming (Legacy)
- This is the original implementation method.
- This method will not support the future BLOB column feature.
PowerSyncDatabase.connect()
method uses WebSocket. You can optionally specify the connectionMethod
to override this:
SQLite Virtual File Systems
This SDK supports multiple Virtual File Systems (VFS), responsible for storing the local SQLite database:1. IDBBatchAtomicVFS (Default)
- This system utilizes IndexedDB as its underlying storage mechanism.
- Multiple tabs are fully supported across most modern browsers.
- Users may experience stability issues when using Safari.
2. OPFS-based Alternatives
PowerSync supports two OPFS (Origin Private File System) implementations that generally offer improved performance:OPFSCoopSyncVFS (Recommended)
- This implementation provides comprehensive multi-tab support across all major browsers.
- It offers the most reliable compatibility with Safari and Safari iOS.
- Example configuration:
AccessHandlePoolVFS
- This implementation delivers optimal performance for single-tab applications.
- The system is not designed to handle multiple tab scenarios.
- The configuration is similar to
OPFSCoopSyncVFS
, but requires usingWASQLiteVFS.AccessHandlePoolVFS
.
VFS Compatibility Matrix
VFS Type | Multi-Tab Support (Standard Browsers) | Multi-Tab Support (Safari/iOS) | Notes |
---|---|---|---|
IDBBatchAtomicVFS | ✅ | ❌ | Default, some Safari stability issues |
OPFSCoopSyncVFS | ✅ | ✅ | Recommended for multi-tab support |
AccessHandlePoolVFS | ❌ | ❌ | Best for single-tab applications |