Support cron triggers using preview and dev

[Kynson]

💡 Feature request

Describe the feature

Currently, there is no way to test scheduled jobs, since we can't fire a scheduled during development. I suggest adding support of "cron triggers testing" for wrangler dev or wrangler preview, which speeds up the development and testing.

Possible methods of triggering a cron job during development:

• For wrangler dev, wrangler creates a special route (path) during development, and developers can trigger a job by sending a request to the route, eg: GET http://127.0.0.1:8787/__crons/:cronExpression
• For wrangler preview, a Test Triggers tab is available for developers to trigger a cron job.

Describe the alternatives

The current work around for this issue is to simply deploy the worker to production.
Or add the code I want to test to the fetch event handler, which is really inconvenient:

addEventListener('scheduled', (event) => {
  event.waitUntil(scheduledJob(event))
});
addEventListener('fetch', (event) => {
  event.respondWith(scheduledJob(event))
})
const scheduledJob = (event) => {
  // Job
}

Thanks.

[Electroid]

Thanks for making this issue! This is definitely something we need to support.

In the interim, a simple workaround would be to call a mock scheduled event from a fetch handler. Not nice, but it can get the job done for you if you need it today.

[Kynson]

Cloudflare recently released miniflare, which supports cron trigger testing. If anyone wants to test cron triggers at the moment, you may refer this link https://miniflare.dev/scheduled.html

Of cause, cron trigger support for wrangler dev/wrangler preview would also be appreciated

[threepointone]

Copy pasting from #738 (comment), where we're landing support for local mode soon.

---

• We've resisted adding miniflare specific features that don't have edge equivalents, but this seems like a good exception to make.
• That said, let's consider this experimental, and not make too much noise about it for now. This will definitely change in the future.
• We could probably make this work on the edge too. For module workers, we could wrap the worker in a facade that exposes a route that triggers the default.scheduled export. For service workers, we'd have to override addEventListener and wrap the fetch handler with our own thing.