# User Identifier & Properties

{% hint style="info" %}
User Identifier Management

User identifiers are used to uniquely identify users. For information on the meaning and importance of user identifiers and criteria for choosing them, refer to the [Managing User Identifiers](/en/getting-started/user-identifier.md) documentation.
{% endhint %}

## User Identifier

### Default Identifiers Provided by Hackle

The JavaScript SDK includes functionality to manage device identifiers. Therefore, users can be automatically identified without separately providing a user identifier.

To retrieve the identifier managed by the SDK, use the following:

```javascript
// 사용자 정보 가지고 오기
const user = hackleClient.getUser();

// 디바이스 식별자 가지고 오기
const deviceId = user.deviceId;

// 내부적으로 관리되는 세션 식별자 가져오기
const sessionId = hackleClient.getSessionId();
```

#### Modifying Device ID

You can inject your own device ID instead of using the device ID provided by Hackle.

```javascript
// 디바이스 식별자 변경
hackleClient.setDeviceId("CUSTOM_DEVICE_ID");
```

#### Setting User Identifier (User ID)

You can set the identifier for a logged-in user.

```javascript
// 로그인 한 사용자 식별자 추가
hackleClient.setUserId("LOGIN_ID");
```

### Additional Identifiers

To add identifier types other than the default identifiers (deviceId, userId), configure as follows:

{% hint style="info" %}
Additional identifiers are not unified into the [Hackle ID](/en/getting-started/user-identifier/hackle-id.md).
{% endhint %}

{% hint style="danger" %}
Using `setUser` overwrites the user information of the current device.

* If you are currently using userId A and do not pass userId A when calling setUser, the userId changes from A to null.
* If you are currently using a custom deviceId and do not pass the current deviceId when calling setUser, the custom deviceId changes to the Hackle deviceId.
* If you are using additional identifiers and do not pass them when calling setUser, the additional identifiers are reset.
* For properties, the cached properties on the device may be retained or reset in the following cases:
  * If the userId and deviceId are the same before and after setUser, the cached properties are retained.
  * If either the userId or deviceId changes before and after setUser, the cached properties are deleted.
    {% endhint %}

```javascript
const user = {
  userId: "LOGIN_ID",           // 사용자 ID (핵클 통합 식별자 사용가능)
  deviceId: "CUSTOM_DEVICE_ID", // 디바이스 ID (핵클 통합 식별자 사용가능)
  identifiers: {
    myCustomId: "CUSTOM_IDENTIFIER" // Custom ID
  }
};

hackleClient.setUser(user);
```

## User Property

The Hackle SDK supports adding user properties.

* Properties must be sent as key-value pairs (Property Key and Property Value).
* The maximum number of properties that can be added is 128.

<table><thead><tr><th width="133.04296875">Category</th><th width="127.60546875">Type</th><th>Constraints</th></tr></thead><tbody><tr><td>Property Key</td><td><code>string</code></td><td><ul><li>Character limit is 128 characters.</li><li>Case-insensitive.</li><li>For example, AGE and age are recognized as the same Property Key.</li></ul></td></tr><tr><td>Property Value</td><td><code>boolean</code>, <code>string</code>, <code>number</code>, <code>array</code></td><td><ul><li>For string type, the character limit is 1024 characters.</li><li>String type is case-sensitive.</li><li>For example, APPLE and apple are recognized as different Property Values.</li><li>For number type, up to 15 integer digits and up to 6 decimal places are supported.</li></ul></td></tr></tbody></table>

### Adding User Properties

You can easily add user properties. Calling the function below works the same as adding a property using `set` in a PropertyOperations object.

```javascript
hackleClient.setUserProperty("gender", "female");
```

### Configuring User Properties

You can add or remove user properties.

<table><thead><tr><th width="150">Supported Functions</th><th>Description</th></tr></thead><tbody><tr><td><code>set</code></td><td>Sets a User Property. If a Property Value already exists for the Property Key, it is overwritten.</td></tr><tr><td><code>setOnce</code></td><td><p>Sets a User Property value only once. If a property already exists for the Property Key, it is ignored.</p><p>For example, you can use this to set a user's registration date or initial sign-up location.</p></td></tr><tr><td><code>unset</code></td><td>Removes a User Property.</td></tr><tr><td><code>clearAll</code></td><td>Removes all User Properties.</td></tr></tbody></table>

Instantiate a `PropertyOperationsBuilder` object with the user properties you want to configure. Then call `updateUserProperties` to update the user properties. You can also configure multiple properties at once.

```javascript
import { PropertyOperationsBuilder } from "@hackler/javascript-sdk"

const operations = new PropertyOperationsBuilder()
    .set("age", 42)
    .set("grade", "GOLD")
    .setOnce("sign_up_date", "2020-07-03")
    .build();

hackleClient.updateUserProperties(operations);
```

## Resetting User

You need to reset previously configured information. Resetting clears all previously configured identifiers and properties.

{% hint style="danger" %}
Resetting a user also resets all user properties stored on the server. If you want to handle logout, use `hackleClient.setUserId(undefined);` instead.

Assigning undefined to userId handles logout on the client side.
{% endhint %}

```javascript
hackleClient.resetUser();
```

Calling `resetUser()` clears all previously configured identifiers and properties.


---

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