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An event says that something happened, like user.created or invoice.paid. Your app emits it, and Nelkap does two things with it:
  • It starts a run of every workflow that listens for the event.
  • It wakes every run waiting on the event’s key.
The code that emits the event doesn’t need to know what happens next. To react to a sign-up in a new way, you add a workflow that listens for user.created, without touching the sign-up code.

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Listen for an event

List the events a workflow listens for when you register it:
A workflow can listen for up to 100 events. Each run it starts gets the event’s payload as its own payload.

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Emit an event

Here, one event starts two runs, one of onboardUser and one of addToNewsletter, both with the payload user_42. emit returns their IDs, or an empty list if no workflow listens for the event. An event takes:
  • event, its name, up to 256 characters.
  • payload, if you want, any JSON value, passed to every run it starts.
  • tags, if you want, up to 10 labels, given to every run it starts.
  • wakeOn, if you want, the key of the runs it wakes.
Name events after what happened, in the past tense, like order.shipped. A name says what happened, never which workflow should run, so the list of listeners can grow freely.

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Wake waiting runs

A run can pause until an event arrives with a given key, using step.wait. To wake it, emit an event with wakeOn set to that key:
Every run waiting on refund_ord_42 goes on, and its step.wait returns the event’s payload. The same event also starts the workflows listening for refund.reviewed, like any event. An event only wakes the runs already waiting when it arrives. See Wait for an event for how to make sure the run is waiting first.

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Emit from a workflow

A workflow can emit events too, for example to let other workflows know that an order shipped. Emit in a step, so the event goes out once, even when the run picks up again later:

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Events from other services

Services like a payment provider can’t call emit, but they can call a URL. A webhook gives you that URL, and turns each call into an event. See Webhooks.

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Follow your events

Every event is listed with its project, the time it arrived, and the number of runs it started, whether your app emitted it or a webhook received it. Filter events by name, by project, by period, or by whether they started any run, for example to find events no workflow listened for.