Alias
Detailed technical description of the Alias API call.
The alias
call lets you merge different identities of a known user.
alias
is an advanced method that lets you change the tracked user's ID explicitly. This method is useful when managing identities for some of the downstream destinations.
The following destinations support the alias
call:
Amplitude (only supported by the JavaScript SDK via Cloud Mode )
Sample payload
A sample payload of an alias
call with most of the Common Fields removed is shown below:
The corresponding event that generates the above payload via the JavaScript SDK is as shown:
The RudderStack SDK automatically passes the user's anonymousId
as previousId
in the payload, as seen above.
When instrumenting a website with the JavaScript SDK, making the alias
call via the client-side is important as the anonymousId
is generated via the browser. Similarly, if you're using a server-side SDK, the alias
call must be made from the server-side as the session ID is set as the anonymousId
.
Alias fields
In addition to the Common Fields, the alias
call accepts the following fields:
Field
Type
Presence
Description
userId
Object
Optional (if anonymousId
is already set)
The user's identifier in your database. Either userId
or anonymousId
should be present.
previousId
String
Required
The user's previous identifier.
userId
vs previousId
userId
vs previousId
The
previousId
attribute refers to the previous user identifier. It could be either:An
anonymousId
assigned to the user (by the browser if the user is a new visitor or has not logged in yet, or the session ID if you're using a server-side SDK).A previously set
userId
to identify the user via theidentify
call.
The
userId
is the user's new identity or an existing identity that you want to merge withpreviousId
.
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