How to create a binding TS types from RPC worker?

https://developers.cloudflare.com/workers/runtime-apis/bindings/service-bindings/#example--build-your-first-service-binding-using-rpc

Following this typescript example,

wrangler types

wrangler types

creates an interface

Env

Env

Env

Env with type

WORKER_B: Fetcher

WORKER_B: Fetcher

WORKER_B: Fetcher

WORKER_B: Fetcher. This leads to bad typing when I want to call

WORKER_B.add()

WORKER_B.add()

WORKER_B.add()

WORKER_B.add(). How this can be improved?

Cloudflare Docs

Service bindings - Runtime APIs · Cloudflare Workers docs

Facilitate Worker-to-Worker communication.

hunt•2/19/25, 11:52 PM

I haven't seen a way to do that in a typegen fashion, but it can be solved by making a edit to the env object in the referencing worker
https://github.com/hntrl/durable-object-rpc-repro/blob/9804eccb6468db2d0363ca86aa1f1e96e63f7c63/packages/workerB/worker-configuration.d.ts#L4
(setting the type parameter of the Fetcher to the class of whatever it is you're trying to access)

GitHub

durable-object-rpc-repro/packages/workerB/worker-configuration.d.ts...

Contribute to hntrl/durable-object-rpc-repro development by creating an account on GitHub.

Hhunt I haven't seen a way to do that in a typegen fashion, but it can be solved by ma...

herenicknameOP•2/20/25, 12:23 AM

Can I call a Durable Object from a worker of another wrangler project? I want to separate DO and api-workers that call them into different projects.

So in this example I want to do this:
/DOs/src/index.ts:

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

  async sayHello(): Promise<string> {
    return "Hello, World!";
  }
}

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

  async sayHello(): Promise<string> {
    return "Hello, World!";
  }
}

/api/src/index.ts:

export default {
  async fetch(request, env) {
    // Every unique ID refers to an individual instance of the Durable Object class
    const id = env.MY_DURABLE_OBJECT.idFromName("foo");

    // A stub is a client used to invoke methods on the Durable Object
    const stub = env.MY_DURABLE_OBJECT.get(id);

    // Methods on the Durable Object are invoked via the stub
    const rpcResponse = await stub.sayHello();

    return new Response(rpcResponse);
  },
} satisfies ExportedHandler<Env>;

export default {
  async fetch(request, env) {
    // Every unique ID refers to an individual instance of the Durable Object class
    const id = env.MY_DURABLE_OBJECT.idFromName("foo");

    // A stub is a client used to invoke methods on the Durable Object
    const stub = env.MY_DURABLE_OBJECT.get(id);

    // Methods on the Durable Object are invoked via the stub
    const rpcResponse = await stub.sayHello();

    return new Response(rpcResponse);
  },
} satisfies ExportedHandler<Env>;

hunt•2/20/25, 1:02 AM

AFAIK not in the way you're describing. you still need to expose some way to access those stubs through an entrypoint on the parent worker of your objects. (i.e. you can't create a binding to a durable object that lives on another worker)

I have a similar want to what you're describing, and something like this is as close as I've come to what I'm hoping for.

/DOs/src/index.ts

export class MyDurableObject extends DurableObject {
  RpcTarget = class extends RpcTarget {
    private object: MyDurableObject

    constructor(object: MyDurableObject) {
      super()
      this.object = object;
    }

    sayHello() {
      // this closure will be called on the DO, so you can access all of the object's state
      return `Hello world from ${this.object.ctx.id.toString()}!`
    }
  }

  getRpcTarget() {
    return new RpcTarget(this)
  }
}

export default class MyEntrypoint extends WorkerEntrypoint {
  async getObject(id: string) {
    const objectId = env.MY_DURABLE_OBJECT.idFromName(id);
    const stub = env.MY_DURABLE_OBJECT.get(objectId);
    return target = stub.getRpcTarget()
  }
}

export class MyDurableObject extends DurableObject {
  RpcTarget = class extends RpcTarget {
    private object: MyDurableObject

    constructor(object: MyDurableObject) {
      super()
      this.object = object;
    }

    sayHello() {
      // this closure will be called on the DO, so you can access all of the object's state
      return `Hello world from ${this.object.ctx.id.toString()}!`
    }
  }

  getRpcTarget() {
    return new RpcTarget(this)
  }
}

export default class MyEntrypoint extends WorkerEntrypoint {
  async getObject(id: string) {
    const objectId = env.MY_DURABLE_OBJECT.idFromName(id);
    const stub = env.MY_DURABLE_OBJECT.get(objectId);
    return target = stub.getRpcTarget()
  }
}

/api/src/index.ts

export default {
  async fetch(request, env) {
    const target = env.MY_OTHER_WORKER.getObject("foo");
    return new Response(await target.sayHello())
  }
}

export default {
  async fetch(request, env) {
    const target = env.MY_OTHER_WORKER.getObject("foo");
    return new Response(await target.sayHello())
  }
}

There's some issues regarding types when using rpc in this fashion (and maybe some inefficiencies, I'm still trying to corner that myself).
workers-and-pages-helpReturning an RpcTarget from a WorkerEntrypoint shows `never` for method return types

Hhunt AFAIK not in the way you're describing. you still need to expose some way to acc...

herenicknameOP•2/20/25, 11:25 AM

thank you!!!

hunt•2/20/25, 8:18 PM

ofc!

How to create a binding TS types from RPC worker?

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