# User Identifier & Properties

{% hint style="info" %}
Managing User Identifiers

User identifiers are used to uniquely identify users. For details on the meaning and importance of user identifiers and guidelines 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 for managing device identifiers. Therefore, users can be identified automatically without providing a separate user identifier.

You can retrieve the identifier managed by the SDK as follows.

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

// 디바이스 식별자 가져오기
const deviceId = getDeviceId();
```

#### Modifying Device ID

You can inject a custom device ID instead of using the device ID provided by Hackle.

```javascript
// 디바이스 식별자 변경
await 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
await hackleClient.setUserId("LOGIN_ID");
```

### Additional Identifiers

To add identifier types other than the default identifiers (deviceId, userId), configure them as shown below.

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

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

* If you are currently using user ID A and call `setUser` without passing user ID A, the userId changes from A to null.
* If you are currently using a custom deviceId and call `setUser` without passing the current deviceId, the custom deviceId reverts to the Hackle deviceId.
* If you are using additional identifiers and call `setUser` without passing them, the additional identifiers are reset.
* For properties, the cached properties on the device may be retained or cleared based on the following cases:
  * If userId and deviceId are the same before and after `setUser`, cached properties are retained.
  * If userId or deviceId changes before and after `setUser`, cached properties are deleted.
    {% endhint %}

```javascript
const prevUser = await hackleClient.getUser();

const user = {
  ...prevUser, // 이전 유저 정보
  userId: "143", // 사용자 ID (핵클 통합 식별자 사용가능)
  deviceId: "ae2182e0", // 디바이스 ID (핵클 통합 식별자 사용가능)
  identifiers: {
    myCustomId: "42" // Custom ID
  }
}

await hackleClient.setUser(user);
```

## User Properties

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 add user properties simply. Calling the function below behaves the same as adding a property using `set` in a PropertyOperations object.

```javascript
await 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/react-native-sdk"

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

await hackleClient.updateUserProperties(operations);
```

## Resetting User

You must reset the previously configured information. Resetting clears all identifiers and properties that were previously set.

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

Assigning `undefined` to userId performs a client-side logout.
{% endhint %}

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


---

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