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Data Persistence in JavaScript SDK

Understand how our JavaScript SDK persists user data stored in cookies or local storage.

  •   4 minute read  

The JavaScript SDK stores persistent user data in the cookies by default. If the cookies are not supported, the SDK uses local storage instead.

By default, the SDK stores all cookies in the top-level domain. It helps you to identify the users visiting websites hosted under a particular sub-domain. For example, if you include the JavaScript SDK in both admin.samplewebsite.com and app.samplewebsite.com, the SDK will store the cookie in samplewebsite.com. However, you can specify the cookie storage location by using the setCookieDomain parameter in the load API options as shown:

rudderanalytics.load(WRITE_KEY, DATA_PLANE_URL, {
  setCookieDomain: "samplewebsite.com",
});
info
Replace the write keyThe write key (or source write key) is a unique identifier for your source. RudderStack uses this key to send events from a source to the specified destination. and data plane URLThe data plane URL is the location where events are routed and sent to the RudderStack backend for processing. You can find this URL in the home page of your RudderStack dashboard. in the snippet with their actual values.

Cookies

The cookie values are encrypted and their length is directly proportional to the values provided to the SDK. Also, all cookie names are prefixed with rl_ and the values are prefixed with RudderEncrypt:. For example, rl_user_id —> RudderEncrypt:U2FsdGVkX1+UKmiooYoGmKdNws7sgmWgGfHe.

The following table lists the cookies used by the JavaScript SDK to store persistent user data:

NameDescriptionClearing mechanism
using the SDK
rl_user_idStores the user ID set via the identify API. All the subsequent event payloads will contain this data unless cleared from the storage.

For example: 4578, USER_001		rudderanalytics.reset()
rl_traitStores the user traits object set via the identify API. All the subsequent event payloads will contain this data unless cleared from the storage.

For example:
{
  email: “alex@example.com”,
  accountType: “pro”,
  country: “US”,
  someObj: {
    key1: val1,
    key2: val2,
  }
}
rudderanalytics.reset()
rl_anonymous_idStores the anonymous ID. By default, it would be the auto-generated unique ID by SDK for each visitor unless overridden via setAnonymousId API. All the subsequent event payloads will contain this data unless cleared from the storage.

For example: 5bfe258f-bd2f-49cf-bddd-8b844f74ab4b, customAnonId		rudderanalytics.reset(true)
rl_group_idStores the user group ID set via the group API. All the subsequent group event payloads will contain this data unless cleared from the storage.

For example: GRP_3, 98		rudderanalytics.reset()
rl_group_traitStores the user group traits object set via the group API. All the subsequent group event payloads will contain this data unless cleared from the storage.

For example:
{
  location: “New Orleans”,
  nationality: “US”,
  someObj: {
    key1: val1,
    key2: val2,
  }
}
rudderanalytics.reset()
rl_page_init_referrerStores the initial referrer of the page when a user visits a site for the first time. All the subsequent event payloads will contain this data.

For example: https://www.google.com/		Cannot be cleared using SDK.
rl_page_init_referring_domainStores the initial referring domain of the page when a user visits a site for the first time. All the subsequent event payloads will contain this data.

For example: google.com		Cannot be cleared using SDK.
test_rudder_cookieChecks whether the cookie storage of a browser is accessible or not. Once checked, the SDK removes the cookie immediately.

For example: test_rudder_cookie:true		Cleared automatically.
rl_sessionStores the session-related information including sessionId if session tracking is enabled.

For example: 1678961874		Manual session tracking: rudderanalytics.endSession()

Automatic session tracking: Automatically cleared by the SDK (if autoTrack: false).
rl_auth_tokenStores the authentication token passed by the user.

For example: MOx2ZmMwLNE2A2IdNKL0N2VhN2I3Z		rudderanalytics.reset()

Local storage

RudderStack stores the local storage cookie names with rudder.<uuid>. prefix where uuid is in the standard UUID v4 format. For example, rudder.2dc2aee6-2836-4273-be69-79c90c04ddec.reclaimEnd.

The JavaScript SDK uses local storage to keep track of the events sent to the RudderStack backend, as listed in the below table:

NameDescription
ackTimer for other browser tabs to claim control of the retry queue.
For example, 1639734070124
reclaimStart and reclaimEndDetermines if a tab takes over the queue from another tab.
For example, 2dc2aee6-2836-4273-be69-79c90c04ddec
inProgressKeeps track of the events in progress. For example:
{
  “d89d7fb5-945e-4378-bda5-492e4b596fb4”: {
   “item”: {
    “url”: “https://rudderstack-dataplane.rudderstack.com/v1/track",
    “headers”: {
     “Content-Type”: “application/json”,
      …
    },
    “message”: { 
     …
    }
    “attemptNumber”: 1,
    “time”: 1639734792773,
    “id”: “a4d89d7f-b594-4eb3-b8bd-a5492e4b596f”
   }
  }
}
queueKeeps track of the events that are in the processing queue. For example:
[
  {
   “item”: {
    “url”: “https://rudderstack-dataplane.rudderstack.com/v1/track”,
    “headers”: {
     “Content-Type”: “application/json”,
      …
    },
    “message”: { 
     …
    }
    “attemptNumber”: 0,
    “time”: 1639734792773,
    “id”: “a4d89d7f-b594-4eb3-b8bd-a5492e4b596f”
   }
  }
]

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