# once

`import { once } from "destack:simulation/scenario";`

Create a trigger that fires once.

```ds title="once"
export function once(on?: EventKind | undefined): Trigger
```

[language/library/src/simulation/scenario/trigger.ds:78:80](https://github.com/destack-sh/destack/blob/main/language/library/src/simulation/scenario/trigger.ds#L78-L80)