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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.

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

Link an alias (e.g. anonymous ID) to a user. Sends $create_alias event.
ParameterTypeRequiredDescription
distinctIdstringyesCurrent user identifier (e.g. after login)
aliasstringyesAlias to link (e.g. previous anonymous ID)
sessionIdstringnoFrom x-signal-session-id header for client correlation
windowIdstringnoFrom 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. 
const { sessionId, windowId, distinctId } = getSessionInfo(req);

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

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Example: Login flow

// 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);
}

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See also