index.js

/**
 * @typedef Bindings
 * @property {DurableObjectNamespace} COUNTER
 */

/**
 * Worker
 */
export default {
	/**
	 * @param {Request} req
	 * @param {Bindings} env
	 * @returns {Promise<Response>}
	 */
	async fetch(req, env) {
		let id = env.COUNTER.idFromName('A');
		let obj = env.COUNTER.get(id);
		let resp = await obj.fetch(req.url);
		let count = await resp.text();

		return new Response("Durable Object 'A' count: " + count);
	},
};

/**
 * Durable Object
 */
export class Counter {
	/**
	 * @param {DurableObjectState} state
	 */
	constructor(state) {
		this.state = state;
	}

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

		// Durable Object storage is automatically cached in-memory, so reading the same key every request is fast.
		// (That said, you could also store the value in a class member if you prefer.)
		/** @type {number} */
		let value = (await this.state.storage.get('value')) || 0;

		switch (url.pathname) {
			case '/increment':
				++value;
				break;
			case '/decrement':
				--value;
				break;
			case '/':
				// Just serve the current value.
				break;
			default:
				return new Response('Not found', { status: 404 });
		}

		// We don't have to worry about a concurrent request having modified the
		// value in storage because "input gates" will automatically protect against
		// unwanted concurrency. So, read-modify-write is safe. For more details,
		// see: https://blog.cloudflare.com/durable-objects-easy-fast-correct-choose-three/
		await this.state.storage.put('value', value);

		return new Response('' + value);
	}
}