> ## 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()

# React — Alias

Link an alias (e.g. anonymous ID) to the current user. Use this to merge anonymous events (from before login) with the identified user. Access via `useSignal()`.

## Accessing the method

Get `alias` from `useSignal()`:

```tsx theme={null}
import { useSignal } from '@signal-js/react';

function LoginHandler({ anonymousId, userId }) {
  const { alias } = useSignal();

  const handleLogin = () => {
    // Link anonymous ID to the identified user
    if (anonymousId) {
      alias(anonymousId);
    }
  };

  return <button onClick={handleLogin}>Log in</button>;
}
```

## alias(alias)

Links an alias to the current user. Sends a `$create_alias` event.

| Parameter | Type     | Required | Description                                |
| --------- | -------- | -------- | ------------------------------------------ |
| `alias`   | `string` | yes      | Alias to link (e.g. previous anonymous ID) |

**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.

## Example: Login flow

```tsx theme={null}
import { useSignal } from '@signal-js/react';
import { useEffect, useState } from 'react';

function LoginFlow() {
  const { identify, alias, distinctId } = useSignal();
  const [anonymousId, setAnonymousId] = useState<string | null>(null);

  useEffect(() => {
    // Store anonymous ID before login
    if (!distinctId) {
      // Get anonymous ID from localStorage or generate one
      const stored = localStorage.getItem('anonymous_id');
      if (stored) {
        setAnonymousId(stored);
      }
    }
  }, [distinctId]);

  const handleLogin = async (userId: string, userTraits: Record<string, unknown>) => {
    // Identify the user
    identify(userId, userTraits);

    // Link anonymous ID if it exists
    if (anonymousId) {
      alias(anonymousId);
      localStorage.removeItem('anonymous_id');
    }
  };

  return (
    <button onClick={() => handleLogin('user_123', { email: 'user@example.com' })}>
      Log in
    </button>
  );
}
```

## How it works

1. **Before login:** User browses anonymously. Events are tracked with an anonymous ID.
2. **After login:** Call `identify(userId, traits)` to set the user's identity.
3. **Link alias:** Call `alias(anonymousId)` to link the anonymous ID to the identified user.
4. **Result:** All events (both anonymous and identified) are now associated with the same user profile.

## See also

* [Identify](/docs/integrations/react/identify) — identify() and reset()
* [Capture](/docs/integrations/react/capture) — Track events