Shared Exports

By default, each client connection has its own isolated state. Shared Exports let multiple clients -- and even other Workers -- share the same state via Durable Objects.

Client-side usage

Add ?shared to the import URL:

import { Counter } from "https://my-worker.workers.dev/?shared";

const counter = await new Counter(0);
await counter.increment();  // 1

Any other client importing with ?shared connects to the same Durable Object and sees the same state:

// Another browser tab, another device, another continent
import { Counter } from "https://my-worker.workers.dev/?shared";
await counter.getCount();  // 1 -- sees the first client's increment
await counter.increment();  // 2

Everything that works in normal mode -- functions, classes, nested objects, streaming, iterators -- works in shared mode.

Worker-side usage

From within another Worker, shared exports are available through native Workers RPC. No serialization overhead, no WebSocket:

import { Counter } from "./.export-shared.js";

const counter = await new Counter(0);
await counter.increment();  // Direct DO RPC call

The .export-shared.js module is generated at build time. It uses import { env } from "cloudflare:workers" to access the Durable Object binding.

Rooms

By default, all shared clients connect to a single room called "default". You can specify a room name to create isolated shared instances:

import { Counter } from "https://my-worker.workers.dev/?shared&room=lobby";
import { Counter } from "https://my-worker.workers.dev/?shared&room=game-1";
// These are separate Durable Object instances

Configuration

Shared exports require Durable Object bindings in wrangler.toml. The create-export template includes these by default:

[durable_objects]
bindings = [
  { name = "SHARED_EXPORT", class_name = "SharedExportDO" }
]

[[migrations]]
tag = "v1"
new_classes = ["SharedExportDO"]

Architecture

Client A ──WebSocket──> Worker (bridge) ──Workers RPC──> Durable Object
Client B ──WebSocket──> Worker (bridge) ──Workers RPC──> ↑ same instance
Worker C ─────────────────────Workers RPC─────────────> ↑ same instance

• Client to DO: The Worker bridges WebSocket messages to the DO via Workers RPC. Only the WebSocket leg uses devalue serialization.
• Worker to DO: Direct Workers RPC -- native V8 serialization, streams and objects pass through natively.
• Concurrency: Durable Objects are single-threaded. Requests are processed sequentially, preventing race conditions.