durable-objects

Extend the DurableObject class from cloudflare:workers and configure a wrangler migration with new_sqlite_classes. Initialize tables inside the constructor using ctx.blockConcurrencyWhile and access storage synchronously via ctx.storage.sql.exec.

Use @cloudflare/vitest-pool-workers with defineWorkersConfig pointing at your wrangler config. Access stubs via env from cloudflare:test, inspect internals with runInDurableObject, and trigger alarms instantly with runDurableObjectAlarm.

Use RPC methods with compatibility date 2024-04-03 or later. Public class methods become typed RPC endpoints callable directly on the stub, giving you type safety that a manual fetch handler lacks.

Storage operations are protected by input and output gates, but fetch and other non-storage I/O allow request interleaving. Use optimistic locking with version numbers or transactions to guard state across external calls.

Avoid Durable Objects for stateless request handling, which plain Workers handle better, and for workloads needing maximum global distribution or high fan-out of independent requests. DOs excel at per-entity coordination and strong consistency.

Each DO supports one alarm at a time, and calling setAlarm replaces any existing alarm. The alarm handler runs with automatic retries on failure, so handlers should be idempotent and can reschedule by calling setAlarm again.