Scheduled Handler

Background

When a Worker is invoked via a Cron Trigger, the scheduled() handler handles the invocation.

Testing scheduled() handlers in local development

You can test the behavior of your scheduled() handler in local development using Wrangler.

Cron Triggers can be tested using Wrangler by passing in the --test-scheduled flag to wrangler dev. This will expose a /__scheduled (or /cdn-cgi/handler/scheduled for Python Workers) route which can be used to test using a http request. To simulate different cron patterns, a cron query parameter can be passed in.

npx wrangler dev --test-scheduled

curl "http://localhost:8787/__scheduled?cron=*+*+*+*+*"

curl "http://localhost:8787/cdn-cgi/handler/scheduled?cron=*+*+*+*+*" # Python Workers

---

Syntax

JavaScript

export default {
  async scheduled(controller, env, ctx) {
    ctx.waitUntil(doSomeTaskOnASchedule());
  },
};

TypeScript

interface Env {}
export default {
  async scheduled(
    controller: ScheduledController,
    env: Env,
    ctx: ExecutionContext,
  ) {
    ctx.waitUntil(doSomeTaskOnASchedule());
  },
};

Python

from workers import handler

@handler
async def on_scheduled(controller, env, ctx):
  ctx.waitUntil(doSomeTaskOnASchedule())

Properties

• controller.cron string

  • The value of the Cron Trigger that started the ScheduledEvent.

• controller.type string

  • The type of controller. This will always return "scheduled".

• controller.scheduledTime number

  • The time the ScheduledEvent was scheduled to be executed in milliseconds since January 1, 1970, UTC. It can be parsed as new Date(controller.scheduledTime).

• env object

  • An object containing the bindings associated with your Worker using ES modules format, such as KV namespaces and Durable Objects.

• ctx object

  • An object containing the context associated with your Worker using ES modules format. Currently, this object just contains the waitUntil function.

Methods

When a Workers script is invoked by a Cron Trigger, the Workers runtime starts a ScheduledEvent which will be handled by the scheduled function in your Workers Module class. The ctx argument represents the context your function runs in, and contains the following methods to control what happens next:

• ctx.waitUntil(promisePromise) : void

  • Use this method to notify the runtime to wait for asynchronous tasks (for example, logging, analytics to third-party services, streaming and caching). The first ctx.waitUntil to fail will be observed and recorded as the status in the Cron Trigger Past Events table. Otherwise, it will be reported as a success.