---
title: User
slug: web-experimentation/api/1pep-user
docTags: 
createdAt: 2026-08-05T20:56:17.000Z
---

Use this API to record the user's values for any number of dimensions or [custom attributes](docId:3kT0et8s5S8T25ZUCKQes). The syntax is identical for both.

:::hint{type="danger"}
**Warning**
The Optimizely Experimentation terms of service prohibit you from sending any personally identifiable information (PII) such as names, social security numbers, email addresses, or any similar data to the Experimentation system through list attributes or other features.
:::

Custom attributes can be used for audience targeting as well as results segmentation.

To use custom attributes for audience targeting and result segmentation, you must first [create the attribute](docId:3kT0et8s5S8T25ZUCKQes) in the Optimizely UI. The `User` API lets you use any API name to set attributes that have not yet been created, but those attribute values are not available for audience targeting or segmentation. If you later create a custom attribute using that same API name, previously stored values are made available for audience targeting and segmentation the next time the Web Experimentation snippet updates.

The values are saved in [`localStorage`](https://developer.mozilla.org/en-US/docs/Web/API/Storage/LocalStorage) and are persisted across sessions, so you do not need to provide them again on future page loads.

### Syntax

```javascript
window["optimizely"].push(user);
```

### Parameters

| Parameter and Type                    | Child Attribute                                 | Description                                                                                                                                                                                                              |
| ------------------------------------- | ----------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| **user** *UserObject*                 | N/A                                             | This is a user object. Required.                                                                                                                                                                                         |
| **type** *string*                     | Child attribute of type `UserObject`.           | This is a static value that indicates that you're using the `user` function. Required.                                                                                                                                   |
| **attributes** *UserCustomAttributes* | Child attribute of type `UserObject`.           | An object that maps custom attribute IDs or custom attribute API names to the user's value for each custom attribute. Custom attribute values must be strings, or `null` if you want to remove the previously set value. |
| `*` *string* or *integer*             | Child attribute of type `UserCustomAttributes`. | You can specify additional properties of your choice.                                                                                                                                                                    |

### Example call

```javascript
window["optimizely"].push({
  "type": "user",
  "attributes": {
    "123": "custom attribute value",
    "customAttributeApiName": "this is also a custom attribute value"
  }
});
```

## Examples

### Specify a custom attribute by ID

You can specify a custom attribute by using its ID as the key for an entry in the `attributes` object. After [create a custom attribute](docId:3kT0et8s5S8T25ZUCKQes) in the Optimizely UI, an ID is generated and displayed in **Audiences > Attributes**.

```javascript
window["optimizely"].push({
  type: "user",
  attributes: {
    123: "gold"
  }
});
```

### Specify a custom attribute by API name

You can specify a custom attribute by using its API name as the key for an entry in the `attributes` object. You provide the API name when [creating a custom attribute](docId:3kT0et8s5S8T25ZUCKQes) in the Optimizely UI in **Audiences > Attributes**.

```javascript
window["optimizely"].push({
  type: "user",
  attributes: {
    frequentFlyerStatus: "gold"
  }
});
```

### Unset a user's custom attribute value

If you want to remove a custom attribute value that had previously been set for a user, you can do that by providing a value of `null`.

```javascript
window["optimizely"].push({
  type: "user",
  attributes: {
    frequentFlyerStatus: null
  }
});
```