api-docs/docs/browser-tracker/markdown/browser-tracker.browsertracker.setuserid.md
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[Home](./index.md) > [@snowplow/browser-tracker](./browser-tracker.md) > [BrowserTracker](./browser-tracker.browsertracker.md) > [setUserId](./browser-tracker.browsertracker.setuserid.md)
## BrowserTracker.setUserId property
Set the business-defined user ID for this user.
<b>Signature:</b>
```typescript
setUserId: (userId?: string | null) => void;
```