TypeScript
The @cloudflare/workers-types package provides the Service and DurableObjectNamespace types, each of which accepts a single type parameter for the server-side WorkerEntrypoint or DurableObject types.
Using higher-order types, we automatically generate client-side stub types (e.g., forcing all methods to be async).
For example:
interface Env {  SUM_SERVICE: Service<SumService>;  COUNTER_OBJECT: DurableObjectNamespace<Counter>
}
export default {  async fetch(req, env, ctx): Promise<Response> {    const result = await env.SUM_SERVICE.sum(1, 2);    return new Response(result.toString());  }
} satisfies ExportedHandler<Env>;