Events

Stop a scheduled or sleeping run when a change makes its remaining work unnecessary. Define cancelOn on the function, then send a matching cancellation event.

Cancel a reminder when it is deleted

This reminder function sleeps until the requested time. A deletion event with the same reminderId cancels the run before it sends the reminder.

import { inngest } from "./client";
import { sendReminder } from "./notifications";

export const scheduleReminder = inngest.createFunction(
  {
    id: "schedule-reminder",
    triggers: { event: "reminders/created" },
    cancelOn: [
      {
        // The event name that cancels this function
        event: "tasks/reminder.deleted", 
        // Ensure the cancellation event (async) and the
        // triggering event (event)'s reminderId are the same:
        if: "async.data.reminderId == event.data.reminderId",
        // only in the first 24h since the function was scheduled.
        // this is optional.
        timeout: "24h",
      },
    ],
  },
  async ({ event, step }) => {
    await step.sleepUntil("wait-until-due", event.data.remindAt);
    await step.run("send-reminder", () => sendReminder(event.data));
  }
);

Let's break down how this works:

1. Whenever the function is triggered, a cancellation listener is created which waits for an "tasks/reminder.deleted" event to be received.
2. The if statement tells Inngest that both the triggering event ("tasks/reminder.created") and the cancellation event ("tasks/reminder.deleted") have the same exact value for data.reminderId in each event payload. This makes sure that an event does not cancel a different reminder.

Expressions

In the expression, event is the original reminders/created trigger and async is the later reminders/deleted event. Compare a stable identifier so one customer's event does not cancel another customer's run. Send the deletion event to Inngest when the reminder is removed. For a direct equality on one field, use match: "data.reminderId" instead of if. You cannot combine match and if in the same cancellation rule.

Tips

• You can also optionally specify a timeout to only enable cancellation for a period of time.
• You can configure multiple events to cancel a function, up to five.
• You can write a more complex matching statement using the if field.
• Bound the cancellation window by adding a timeout rule.
• The canceled run emits inngest/function.cancelled.
• Use Timeouts for elapsed-time limits and Bulk cancellation to stop a selected set of existing runs.

Limits

• A function can listen for up to five cancellation events.
• Cancellation takes effect between steps. It can stop the reminder while the run sleeps, but it cannot interrupt a step.run that has already begun sending it.