This page describes the PowerSync client SDK for Node.js. If you’re interested in using PowerSync for your Node.js backend, no special package is required. Instead, follow our guides on app backend setup.

Source Code

Refer to packages/node in the powersync-js repo on GitHub.

Example Project

A small CLI app showcasing bidirectional sync.

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SDK Features

  • Provides real-time streaming of database changes.
  • Offers direct access to the SQLite database, enabling the use of SQL on both client and server sides.
  • Operations run on a background worker and are asynchronous by default, enabling concurrent queries.
  • Enables subscription to queries for receiving live updates.
  • Eliminates the need for client-side database migrations as these are managed automatically.

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Quickstart

To start using PowerSync in a Node client, first add the dependencies:

npm install @powersync/node

Depending on the package manager used, you might have to approve install scripts. PowerSync currently requires install scripts on the @powersync/node and @powersync/better-sqlite3 packages to download native addons.

Next, make sure that you have:

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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). You can use this example as a reference when defining your schema.

Generate schema automatically

In the dashboard, the schema can be generated based off your sync rules by right-clicking on an instance and selecting Generate client-side schema. Select JavaScript and replace the suggested import with @powersync/node.

Similar functionality exists in the CLI.

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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:

import { PowerSyncDatabase } from '@powersync/node';
import { Connector } from './Connector';
import { AppSchema } from './Schema';

export const db = new PowerSyncDatabase({
  // The schema you defined in the previous step
  schema: AppSchema,
  database: {
    // Filename for the SQLite database — it's important to only instantiate one instance per file.
    dbFilename: 'powersync.db',
    // Optional. Directory where the database file is located.'
    // dbLocation: 'path/to/directory'
  },
});

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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:

  1. Retrieve an auth token to connect to the PowerSync instance.
  2. Apply local changes on your backend application server (and from there, to Postgres)

Accordingly, the connector must implement two methods:

  1. 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.
  2. PowerSyncBackendConnector.uploadData - Use this to upload client-side changes to your app backend. -> See Writing Client Changes for considerations on the app backend implementation.

Example:

import { UpdateType } from '@powersync/node';

export class Connector implements PowerSyncBackendConnector {
    constructor() {
        // Setup a connection to your server for uploads
        this.serverConnectionClient = TODO;
    }

    async fetchCredentials() {
        // Implement fetchCredentials to obtain a JWT from your authentication service.
        // See https://docs.powersync.com/installation/authentication-setup
        // If you're using Supabase or Firebase, you can re-use the JWT from those clients, see
        // - https://docs.powersync.com/installation/authentication-setup/supabase-auth
        // - https://docs.powersync.com/installation/authentication-setup/firebase-auth
        return {
            endpoint: '[Your PowerSync instance URL or self-hosted endpoint]',
            // Use a development token (see Authentication Setup https://docs.powersync.com/installation/authentication-setup/development-tokens) to get up and running quickly
            token: 'An authentication token'
        };
    }

    async uploadData(database) {
      // Implement uploadData to send local changes to your backend service.
      // You can omit this method if you only want to sync data from the database to the client

      // See example implementation here: https://docs.powersync.com/client-sdk-references/javascript-web#3-integrate-with-your-backend
    }
}

With your database instantiated and your connector ready, call connect to start the synchronization process:

await db.connect(new Connector());
await db.waitForFirstSync(); // Optional, to wait for a complete snapshot of data to be available

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Usage

After connecting the client database, it is ready to be used. The API to run queries and updates is identical to our web SDK:

// Use db.get() to fetch a single row:
console.log(await db.get('SELECT powersync_rs_version();'));

// Or db.all() to fetch all:
console.log(await db.all('SELECT * FROM lists;'));

// Use db.watch() to watch queries for changes:
const watchLists = async () => {
  for await (const rows of db.watch('SELECT * FROM lists;')) {
    console.log('Has todo lists', rows.rows!._array);
  }
};
watchLists();

// And db.execute for inserts, updates and deletes:
await db.execute(
  "INSERT INTO lists (id, created_at, name, owner_id) VALUEs (uuid(), datetime('now'), ?, uuid());",
  ['My new list']
);

PowerSync runs queries asynchronously on a background pool of workers and automatically configures WAL to allow a writer and multiple readers to operate in parallel.

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