npm create cloudflare@latest my-durable-app -- \
  --template=cloudflare/durable-objects-template \
  --ts \
  --git \
  --deploy false

cd my-durable-app
npm install
npm run dev

cd my-existing-worker
npm install -D @cloudflare/workers-types

import { DurableObject } from 'cloudflare:workers';

export class Counter extends DurableObject {
  async increment(): Promise<number> {
    // Get current value from storage (default to 0)
    let value: number = (await this.ctx.storage.get('value')) || 0;

    // Increment
    value += 1;

    // Save back to storage
    await this.ctx.storage.put('value', value);

    return value;
  }

  async get(): Promise<number> {
    return (await this.ctx.storage.get('value')) || 0;
  }
}

// CRITICAL: Export the class
export default Counter;

{
  "$schema": "node_modules/wrangler/config-schema.json",
  "name": "my-worker",
  "main": "src/index.ts",
  "compatibility_date": "2025-10-22",

  // Durable Objects binding
  "durable_objects": {
    "bindings": [
      {
        "name": "COUNTER",           // How you access it: env.COUNTER
        "class_name": "Counter"      // MUST match exported class name
      }
    ]
  },

  // REQUIRED: Migration for new DO class
  "migrations": [
    {
      "tag": "v1",                   // Unique migration identifier
      "new_sqlite_classes": [        // Use SQLite backend (recommended)
        "Counter"
      ]
    }
  ]
}

import { Counter } from './counter';

interface Env {
  COUNTER: DurableObjectNamespace<Counter>;
}

export { Counter };

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    // Get Durable Object stub by name
    const id = env.COUNTER.idFromName('global-counter');
    const stub = env.COUNTER.get(id);

    // Call RPC method on the DO
    const count = await stub.increment();

    return new Response(`Count: ${count}`);
  },
};

npx wrangler deploy

import { DurableObject } from 'cloudflare:workers';

export class MyDurableObject extends DurableObject {
  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);

    // Optional: Initialize from storage
    ctx.blockConcurrencyWhile(async () => {
      // Load state before handling requests
      this.someValue = await ctx.storage.get('someKey') || defaultValue;
    });
  }

  // RPC methods (recommended)
  async myMethod(): Promise<string> {
    return 'Hello from DO!';
  }

  // Optional: HTTP fetch handler
  async fetch(request: Request): Promise<Response> {
    return new Response('Hello from DO fetch!');
  }
}

// CRITICAL: Export the class
export default MyDurableObject;

constructor(ctx: DurableObjectState, env: Env) {
  super(ctx, env);  // REQUIRED

  // Access to environment bindings
  this.env = env;

  // this.ctx provides:
  // - this.ctx.storage      (storage API)
  // - this.ctx.id           (unique ID)
  // - this.ctx.waitUntil()  (background tasks)
  // - this.ctx.acceptWebSocket() (WebSocket hibernation)
}

// Export as default (required for Worker to use it)
export default MyDurableObject;

// Also export as named export (for type inference in Worker)
export { MyDurableObject };

// Import the class for types
import { MyDurableObject } from './my-durable-object';

// Export it so Worker can instantiate it
export { MyDurableObject };

interface Env {
  MY_DO: DurableObjectNamespace<MyDurableObject>;
}

{
  "migrations": [
    {
      "tag": "v1",
      "new_sqlite_classes": ["MyDurableObject"]  // ← Use this for SQLite
    }
  ]
}

import { DurableObject } from 'cloudflare:workers';

export class MyDurableObject extends DurableObject {
  sql: SqlStorage;

  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
    this.sql = ctx.storage.sql;

    // Create table on first run
    this.sql.exec(`
      CREATE TABLE IF NOT EXISTS messages (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        text TEXT NOT NULL,
        user TEXT NOT NULL,
        created_at INTEGER NOT NULL
      );

      CREATE INDEX IF NOT EXISTS idx_created_at ON messages(created_at);
    `);
  }

  async addMessage(text: string, user: string): Promise<number> {
    // Insert with exec (returns cursor)
    const cursor = this.sql.exec(
      'INSERT INTO messages (text, user, created_at) VALUES (?, ?, ?) RETURNING id',
      text,
      user,
      Date.now()
    );

    const row = cursor.one<{ id: number }>();
    return row.id;
  }

  async getMessages(limit: number = 50): Promise<any[]> {
    const cursor = this.sql.exec(
      'SELECT * FROM messages ORDER BY created_at DESC LIMIT ?',
      limit
    );

    // Convert cursor to array
    return cursor.toArray();
  }

  async deleteOldMessages(beforeTimestamp: number): Promise<void> {
    this.sql.exec(
      'DELETE FROM messages WHERE created_at < ?',
      beforeTimestamp
    );
  }
}

// Execute query (returns cursor)
const cursor = this.sql.exec('SELECT * FROM table WHERE id = ?', id);

// Get single row
const row = cursor.one<RowType>();

// Get first row or null
const row = cursor.one<RowType>({ allowNone: true });

// Get all rows as array
const rows = cursor.toArray<RowType>();

// Iterate cursor
for (const row of cursor) {
  // Process row
}

// Transactions (synchronous)
this.ctx.storage.transactionSync(() => {
  this.sql.exec('INSERT INTO table1 ...');
  this.sql.exec('UPDATE table2 ...');
  // All or nothing
});

import { DurableObject } from 'cloudflare:workers';

export class MyDurableObject extends DurableObject {
  async increment(): Promise<number> {
    // Get value
    let count = await this.ctx.storage.get<number>('count') || 0;

    // Increment
    count += 1;

    // Put value back
    await this.ctx.storage.put('count', count);

    return count;
  }

  async batchOperations(): Promise<void> {
    // Get multiple keys
    const map = await this.ctx.storage.get<number>(['key1', 'key2', 'key3']);

    // Put multiple keys
    await this.ctx.storage.put({
      key1: 'value1',
      key2: 'value2',
      key3: 'value3',
    });

    // Delete key
    await this.ctx.storage.delete('key1');

    // Delete multiple keys
    await this.ctx.storage.delete(['key2', 'key3']);
  }

  async listKeys(): Promise<string[]> {
    // List all keys
    const map = await this.ctx.storage.list();
    return Array.from(map.keys());

    // List with prefix
    const mapWithPrefix = await this.ctx.storage.list({
      prefix: 'user:',
      limit: 100,
    });
  }

  async deleteAllStorage(): Promise<void> {
    // Delete alarm first (if set)
    await this.ctx.storage.deleteAlarm();

    // Delete all storage (DO will cease to exist after shutdown)
    await this.ctx.storage.deleteAll();
  }
}

// Get single value
const value = await this.ctx.storage.get<T>('key');

// Get multiple values (returns Map)
const map = await this.ctx.storage.get<T>(['key1', 'key2']);

// Put single value
await this.ctx.storage.put('key', value);

// Put multiple values
await this.ctx.storage.put({ key1: value1, key2: value2 });

// Delete single key
await this.ctx.storage.delete('key');

// Delete multiple keys
await this.ctx.storage.delete(['key1', 'key2']);

// List keys
const map = await this.ctx.storage.list<T>({
  prefix: 'user:',
  limit: 100,
  reverse: false
});

// Delete all (atomic on SQLite, may be partial on KV backend)
await this.ctx.storage.deleteAll();

// Transactions (async)
await this.ctx.storage.transaction(async (txn) => {
  await txn.put('key1', value1);
  await txn.put('key2', value2);
  // All or nothing
});

import { DurableObject } from 'cloudflare:workers';

export class ChatRoom extends DurableObject {
  sessions: Map<WebSocket, { userId: string; username: string }>;

  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);

    // Restore WebSocket connections after hibernation
    this.sessions = new Map();

    ctx.getWebSockets().forEach((ws) => {
      // Deserialize attachment (persisted metadata)
      const attachment = ws.deserializeAttachment();
      this.sessions.set(ws, attachment);
    });
  }

  async fetch(request: Request): Promise<Response> {
    // Expect WebSocket upgrade request
    const upgradeHeader = request.headers.get('Upgrade');
    if (upgradeHeader !== 'websocket') {
      return new Response('Expected websocket', { status: 426 });
    }

    // Create WebSocket pair
    const webSocketPair = new WebSocketPair();
    const [client, server] = Object.values(webSocketPair);

    // Get user info from URL or headers
    const url = new URL(request.url);
    const userId = url.searchParams.get('userId') || 'anonymous';
    const username = url.searchParams.get('username') || 'Anonymous';

    // Accept WebSocket with hibernation
    // CRITICAL: Use ctx.acceptWebSocket(), NOT ws.accept()
    this.ctx.acceptWebSocket(server);

    // Serialize metadata to persist across hibernation
    const metadata = { userId, username };
    server.serializeAttachment(metadata);

    // Track in-memory (will be restored after hibernation)
    this.sessions.set(server, metadata);

    // Notify others
    this.broadcast(`${username} joined`, server);

    // Return client WebSocket to browser
    return new Response(null, {
      status: 101,
      webSocket: client,
    });
  }

  // Called when WebSocket receives a message
  async webSocketMessage(ws: WebSocket, message: string | ArrayBuffer): Promise<void> {
    const session = this.sessions.get(ws);

    if (typeof message === 'string') {
      const data = JSON.parse(message);

      if (data.type === 'chat') {
        // Broadcast to all connections
        this.broadcast(`${session?.username}: ${data.text}`, ws);
      }
    }
  }

  // Called when WebSocket closes
  async webSocketClose(ws: WebSocket, code: number, reason: string, wasClean: boolean): Promise<void> {
    const session = this.sessions.get(ws);
    this.sessions.delete(ws);

    // Close the WebSocket
    ws.close(code, 'Durable Object closing WebSocket');

    // Notify others
    if (session) {
      this.broadcast(`${session.username} left`);
    }
  }

  // Called on WebSocket errors
  async webSocketError(ws: WebSocket, error: any): Promise<void> {
    console.error('WebSocket error:', error);
    const session = this.sessions.get(ws);
    this.sessions.delete(ws);
  }

  // Helper to broadcast to all connections
  broadcast(message: string, except?: WebSocket): void {
    this.sessions.forEach((session, ws) => {
      if (ws !== except && ws.readyState === WebSocket.OPEN) {
        ws.send(JSON.stringify({ type: 'message', text: message }));
      }
    });
  }
}

// Receive message from client
async webSocketMessage(
  ws: WebSocket,
  message: string | ArrayBuffer
): Promise<void> {
  // Handle message
}

// WebSocket closed by client
async webSocketClose(
  ws: WebSocket,
  code: number,
  reason: string,
  wasClean: boolean
): Promise<void> {
  // Cleanup
}

// WebSocket error occurred
async webSocketError(
  ws: WebSocket,
  error: any
): Promise<void> {
  // Handle error
}

// ✅ CORRECT: Use ctx.acceptWebSocket (enables hibernation)
this.ctx.acceptWebSocket(server);

// ❌ WRONG: Don't use ws.accept() (standard API, no hibernation)
server.accept();

// ✅ CORRECT: Persist metadata across hibernation
server.serializeAttachment({ userId: '123', username: 'Alice' });

// ✅ CORRECT: Restore metadata in constructor
constructor(ctx, env) {
  super(ctx, env);

  ctx.getWebSockets().forEach((ws) => {
    const metadata = ws.deserializeAttachment();
    this.sessions.set(ws, metadata);
  });
}

// ❌ WRONG: Don't use setTimeout/setInterval (prevents hibernation)
setTimeout(() => { /* ... */ }, 1000);  // ❌ NEVER DO THIS

// ✅ CORRECT: Use alarms for scheduled tasks
await this.ctx.storage.setAlarm(Date.now() + 60000);

import { DurableObject } from 'cloudflare:workers';

export class Batcher extends DurableObject {
  buffer: string[];

  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);

    ctx.blockConcurrencyWhile(async () => {
      // Restore buffer from storage
      this.buffer = await ctx.storage.get('buffer') || [];
    });
  }

  async addItem(item: string): Promise<void> {
    this.buffer.push(item);
    await this.ctx.storage.put('buffer', this.buffer);

    // Schedule alarm for 10 seconds from now (if not already set)
    const currentAlarm = await this.ctx.storage.getAlarm();
    if (currentAlarm === null) {
      await this.ctx.storage.setAlarm(Date.now() + 10000);
    }
  }

  // Called when alarm fires
  async alarm(alarmInfo: { retryCount: number; isRetry: boolean }): Promise<void> {
    console.log(`Alarm fired (retry count: ${alarmInfo.retryCount})`);

    // Process batch
    if (this.buffer.length > 0) {
      await this.processBatch(this.buffer);

      // Clear buffer
      this.buffer = [];
      await this.ctx.storage.put('buffer', []);
    }

    // Alarm is automatically deleted after successful execution
  }

  async processBatch(items: string[]): Promise<void> {
    // Send to external API, write to database, etc.
    console.log(`Processing ${items.length} items:`, items);
  }
}

// Set alarm to fire at specific timestamp
await this.ctx.storage.setAlarm(Date.now() + 60000);  // 60 seconds from now

// Set alarm to fire at specific date
await this.ctx.storage.setAlarm(new Date('2025-12-31T23:59:59Z'));

// Get current alarm (null if not set)
const alarmTime = await this.ctx.storage.getAlarm();

// Delete alarm
await this.ctx.storage.deleteAlarm();

// Alarm handler (called when alarm fires)
async alarm(alarmInfo: { retryCount: number; isRetry: boolean }): Promise<void> {
  // Do work
}

async alarm(alarmInfo: { retryCount: number; isRetry: boolean }): Promise<void> {
  if (alarmInfo.retryCount > 3) {
    console.error('Alarm failed after 3 retries, giving up');
    return;
  }

  try {
    // Idempotent operation (safe to retry)
    await this.sendNotification();
  } catch (error) {
    console.error('Alarm failed:', error);
    throw error;  // Will trigger retry
  }
}