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Create and review Cloudflare Durable Objects. Use when building stateful coordination (chat rooms, multiplayer games, booking systems), implementing RPC methods, SQLite storage, alarms, WebSockets, or reviewing DO code for best practices. Covers Workers integration, wrangler config, and testing with Vitest.
npx skill4agent add cloudflare/cloudflare-docs durable-objects@cloudflare/vitest-pool-workers./references/rules.md./references/testing.md./references/workers.mdblockConcurrencyWhileidFromNamegetByNamesetAlarmsql.exec| Need | Example |
|---|---|
| Coordination | Chat rooms, multiplayer games, collaborative docs |
| Strong consistency | Inventory, booking systems, turn-based games |
| Per-entity storage | Multi-tenant SaaS, per-user data |
| Persistent connections | WebSockets, real-time notifications |
| Scheduled work per entity | Subscription renewals, game timeouts |
// wrangler.jsonc
{
"durable_objects": {
"bindings": [{ "name": "MY_DO", "class_name": "MyDurableObject" }]
},
"migrations": [{ "tag": "v1", "new_sqlite_classes": ["MyDurableObject"] }]
}import { DurableObject } from "cloudflare:workers";
export interface Env {
MY_DO: DurableObjectNamespace<MyDurableObject>;
}
export class MyDurableObject extends DurableObject<Env> {
constructor(ctx: DurableObjectState, env: Env) {
super(ctx, env);
ctx.blockConcurrencyWhile(async () => {
this.ctx.storage.sql.exec(`
CREATE TABLE IF NOT EXISTS items (
id INTEGER PRIMARY KEY AUTOINCREMENT,
data TEXT NOT NULL
)
`);
});
}
async addItem(data: string): Promise<number> {
const result = this.ctx.storage.sql.exec<{ id: number }>(
"INSERT INTO items (data) VALUES (?) RETURNING id",
data
);
return result.one().id;
}
}
export default {
async fetch(request: Request, env: Env): Promise<Response> {
const stub = env.MY_DO.getByName("my-instance");
const id = await stub.addItem("hello");
return Response.json({ id });
},
};getByName()new_sqlite_classesblockConcurrencyWhile()setAlarm()blockConcurrencyWhile()awaitblockConcurrencyWhile()fetch()// Deterministic - preferred for most cases
const stub = env.MY_DO.getByName("room-123");
// From existing ID string
const id = env.MY_DO.idFromString(storedIdString);
const stub = env.MY_DO.get(id);
// New unique ID - store mapping externally
const id = env.MY_DO.newUniqueId();
const stub = env.MY_DO.get(id);// SQL (synchronous, recommended)
this.ctx.storage.sql.exec("INSERT INTO t (c) VALUES (?)", value);
const rows = this.ctx.storage.sql.exec<Row>("SELECT * FROM t").toArray();
// KV (async)
await this.ctx.storage.put("key", value);
const val = await this.ctx.storage.get<Type>("key");// Schedule (replaces existing)
await this.ctx.storage.setAlarm(Date.now() + 60_000);
// Handler
async alarm(): Promise<void> {
// Process scheduled work
// Optionally reschedule: await this.ctx.storage.setAlarm(...)
}
// Cancel
await this.ctx.storage.deleteAlarm();import { env } from "cloudflare:test";
import { describe, it, expect } from "vitest";
describe("MyDO", () => {
it("should work", async () => {
const stub = env.MY_DO.getByName("test");
const result = await stub.addItem("test");
expect(result).toBe(1);
});
});