Source: https://datafa.st/docs/user-identification Markdown source: https://datafa.st/docs/user-identification.md Description: Turn visitors into profiles by identifying them with unique user IDs. Track user journeys across browsers and devices. # User identification Turn anonymous visitors into persistent and searchable **profiles** along with custom parameters. ![Visitor profile and journey](/user-identification.png) Profiles track your users with persistent IDs (like `email` or `userId`) and provide several advantages: - **Cross-platform tracking:** Follow users across browsers and devices - **Search visitors:** Find specific users and their journeys in your analytics dashboard - **Persistent tracking:** Maintain user journey even if cookies are reset - **Better attribution:** Link anonymous traffic to known users ## How to identify a user Use the `window.datafast()` method to identify a visitor: ```javascript window?.datafast("identify", { user_id: "unique-user-id", // required name: "John Wayne", // optional - if present, it will replace the anonymous name in the visitor profile image: "https://example.com/avatar.jpg", // optional - profile image URL // ... any other custom parameters you want to track }); ``` #### Required parameters - **`user_id`** (string, required): A unique identifier for the user like _email_ or _userId_ #### Special parameters (optional) - **`name`** (string): If present, it will replace the anonymous name in the visitor profile - **`image`** (string, 250 char. max.): A valid URL pointing to a profile image to display in [Journeys](/changelog/goal-tracking) and the [Realtime Map](/changelog/real-time-map). Example: `https://lh3.googleusercontent.com/-WuQbhWk1Xso/AAAAAAAAAAI/AAAAAAAAAAA/ALKGfklNb9VSEpE-xxOXfgy6n9NGIdz-2g/photo.jpg?sz=46` #### Custom parameters validation rules - **Property names:** lowercase letters, numbers, underscores (_), and hyphens (-) only. Max 64 characters. - **Property values:** any string, max 255 characters. - **Limits:** maximum 10 custom parameters. ### Ensure reliable tracking (recommended) Add this script to your HTML `` to guarantee identification is captured even when triggered before the main script loads: ```html ``` ## Example usage ```jsx useEffect(() => { if (user && user.email) { window?.datafast("identify", { user_id: user.email, name: user.name, image: user.profileImage, role: user.role, plan: user.plan, }); } }, [user]); ``` > **Note:** User identification is separate from [custom goals](/docs/custom-goals). Use identify to link users to their accounts, and use custom goals to track specific user actions. ## Special notes - **Persistent tracking:** You need to identify the visitor each time their cookie changes for persistent tracking. You can call `window.datafast("identify")` every time their session changes. - **Revenue attribution:** If [revenue attribution](/docs/revenue-attribution-guide) is present, we automatically identify the customer using data from the payment provider.