mParticle’s JavaScript SDK stores certain data points in persistence in order to retain user and session data in between page loads. These data points are sent to the mParticle server whenever an action is logged.

By default, persistence data is stored in localStorage. However, you can configure the SDK to use cookies instead by setting useCookieStorage to true in the SDK configuration. See our Advanced Setup instructions.

An important exception is the cartProducts array, which stores details of products in the customer cart. This is always kept in localStorage, even if useCookieStorage is true, since a large number of items in a cart could otherwise impact cookie size.

The following data points are kept in persistence. To save space, keys will only be stored if there is a non-null value.

Key Value Description
sessionId string The ID of the current session
isEnabled boolean Boolean for if mParticle should log data or not
sessionAttributes object Attributes for the current session
userAttributes object Attributes for the current user
userIdentities array Identities for the current user
serverSettings object Server settings to be sent to mParticle with each logging attempt
devToken string Client token
mpid string mParticle unique identifier
clientId string A unique identifier mParticle uses to generate the mpid
deviceId string A unique identifier for the browser being used
cartProducts array Products in the customer cart - this is always stored in localStorage
dateLastEventSent number Time of the last logged event
cookieSyncDates object Contains times of last cookie sync