api-docs/docs/node-tracker/markdown/node-tracker.adimpressionevent.impressionid.md
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[Home](./index.md) > [@snowplow/node-tracker](./node-tracker.md) > [AdImpressionEvent](./node-tracker.adimpressionevent.md) > [impressionId](./node-tracker.adimpressionevent.impressionid.md)
## AdImpressionEvent.impressionId property
Identifier for the particular impression instance
<b>Signature:</b>
```typescript
impressionId?: string;
```