Durable Objects Rollup ES modules template

export class Counter {
  constructor(state, env) {
    this.state = state;
  }

  // Handle HTTP requests from clients.
  async fetch(request) {
    // Apply requested action.
    let url = new URL(request.url);

    // Durable Object storage is automatically cached in-memory.
    // Reading the same key every request is fast. 
    // You could also store the value in a class member.
    let value = await this.state.storage.get("value") || 0;
    switch (url.pathname) {
    case "/increment":
      ++value;
      break;
    case "/decrement":
      --value;
      break;
    case "/":
      // Serves the current value.
      break;
    default:
      return new Response("Not found", {status: 404});
    }

    // You do not have to worry about a concurrent request having modified the value in storage. 
    // "input gates" will automatically protect against unwanted concurrency. 
    // Read-modify-write is safe. 
    await this.state.storage.put("value", value);

    return new Response(value);
  }
}