> ## Documentation Index
> Fetch the complete documentation index at: https://docs.zeotap.com/llms.txt
> Use this file to discover all available pages before exploring further.

# persistenceInCookieStorage

> Control storage mechanism (cookie vs. local storage).

<Warning>
  **Important:** Please ensure your CMP configuration includes new **Vendor ID 1469** for 1st Party data tracking. Additionally, include **Vendor ID 301** if cookie sync is enabled. [Learn more](/articles/sdks/web-js/configurations/consent-options#shouldcheckzeotapvendorconsent)
</Warning>

**Type:** `Boolean`

**Default:** `false`

**Description:**

This configuration option determines the browser storage mechanism used by the Zeotap SDK to persist user identities and consent information between page loads and sessions.

* **`false` (Default):** The SDK utilizes `sessionStorage`. This is generally suitable for most cases, offering potentially larger storage capacity and not being automatically sent with network requests.
* **`true`:** The SDK utilizes `cookieStorage`.

**Why Use `cookieStorage` (`true`)?**

The primary reason to set `persistenceInCookieStorage: true` is for **cross-subdomain persistence**.

* If your website operates across multiple subdomains (e.g., `www.example.com`, `shop.example.com`, `app.example.com`) and you need the user's identity or consent status set on one subdomain to be recognized on another, you must use cookie storage.
* `sessionStorage` is scoped strictly to the origin (protocol + hostname + port) and cannot be shared across subdomains this way.

**Considerations:**

* **Storage Limits:** Cookies generally have smaller storage limits per domain compared to `sessionStorage`.
* **Network Overhead:** Cookies are automatically included in the headers of every HTTP request sent to the domain they are set for. This can add minor overhead to network traffic. `sessionStorage` data is not sent automatically.
* **Session Persistence**: In `sessionStorage` data is only persisted for the particular session. `cookieStorage` stores the data for subsequent sessions as well.

**Example:**

```jsx title="SDK Initialization for Cross-Subdomain Cookie Storage" theme={null}
window.zeotap.init("YOUR_WRITE_KEY", {
  persistenceInCookieStorage: true, // Use cookie storage
});
```

<Note>
  **ZI Stamping**

  ZI is always stamped in cookie storage irrespective of this option's value. In case, cookie storage is not available, then ZI is stamped in local storage.
</Note>

Try out this <a href="https://github.com/zeotap/zeotap-web-sdk-docs/tree/main/my-docs/static/examples/configurations/persistenceInCookieStorage" target="_blank">example</a>.