> ## Documentation Index
> Fetch the complete documentation index at: https://docs.trysignal.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Alias

> Link an alias to a user with signal.alias()

# Node — Alias

Link an alias (e.g. anonymous ID) to a user with `signal.alias()`. Use when merging anonymous and identified users (e.g. after login). Sends `$create_alias`.

## alias(distinctId, alias, sessionId?, windowId?)

Link an alias (e.g. anonymous ID) to a user. Sends `$create_alias` event.

| Parameter    | Type     | Required | Description                                              |
| ------------ | -------- | -------- | -------------------------------------------------------- |
| `distinctId` | `string` | yes      | Current user identifier (e.g. after login)               |
| `alias`      | `string` | yes      | Alias to link (e.g. previous anonymous ID)               |
| `sessionId`  | `string` | no       | From `x-signal-session-id` header for client correlation |
| `windowId`   | `string` | no       | From `x-signal-window-id` header for client correlation  |

**When to use:** After login to merge anonymous events (from before login) with the identified user. This ensures all events are associated with the same user profile.

```typescript theme={null}
const { sessionId, windowId, distinctId } = getSessionInfo(req);

signal.alias(
  distinctId || userId,
  anonymousId,
  sessionId,
  windowId
);
```

## Example: Login flow

```typescript theme={null}
// After user logs in
const { sessionId, windowId, distinctId } = getSessionInfo(req);

// Identify the user
signal.identify({
  distinctId: userId,
  properties: { email: user.email, name: user.name },
  sessionId,
  windowId,
});

// Link anonymous ID if it exists
if (anonymousId) {
  signal.alias(userId, anonymousId, sessionId, windowId);
}
```

## See also

* [Identify](/docs/integrations/node/identify) — identify()
* [Capture](/docs/integrations/node/capture) — capture()