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Added a note on handling Activity Cancellation in TypeScript SDK #3985

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Added a note on handling Activity Cancellation in TypeScript SDK #3985

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13 changes: 13 additions & 0 deletions docs/develop/typescript/failure-detection.mdx
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Expand Up @@ -238,6 +238,19 @@ If the Temporal Service does not receive a Heartbeat within a [Heartbeat Timeout
Activity Cancellations are delivered to Activities from the Temporal Service when they Heartbeat.
Activities that don't Heartbeat can't get notified of Cancellation requests.

:::note Handling Activity Cancellation
In the TypeScript SDK, Activity implementations must opt in to observe cancellation.

Use one of the following in your Activity to be notified of cancellation:
- `await Context.current().cancelled` — rejects with `CancelledFailure`.
- `await Context.current().sleep(ms)` — rejects on cancellation.
- Pass `Context.current().cancellationSignal` (an `AbortSignal`) to libraries that support abort.

> **Important:** Activities receive cancellation notifications when they heartbeat; if an Activity doesn’t heartbeat, delivery of the cancellation notification can be delayed.

See [Activity namespace reference](https://typescript.temporal.io/api/namespaces/activity#cancellation) and [Context API](https://typescript.temporal.io/api/classes/activity.Context) for more information.
:::

Heartbeats may not always be sent to the Temporal Service—they may be [throttled](/encyclopedia/detecting-activity-failures#throttling) by the Worker.
Heartbeat throttling may lead to Cancellation getting delivered later than expected.

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