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

# Client SDK (Frontend) Reference

## Authorization

You'll need to fetch a `userToken` and provide this when initializing the Kana JS Client instance in order for calls to be successfully made. We have a handy guide which goes into further detail on how to obtain and provide this.

[Authorization (Frontend)](/client-sdk-frontend/authorization-frontend)

## Errors

We return errors within the `error` field of a request. You can use the following to assign the relevant fields to a `data` or `error` variable and check against them to understand if problems occurred or if data was returned:

```javascript theme={null}
const { data, error } = await userClient.canUseFeature("test-feature-id");
```

You can then decide to handle these however you feel is necessary.

### Handling

You can provide the `onError` argument with an async function when initializing the client in order to globally take actions when errors occur. The following example logs all errors upon one occurring:

```javascript theme={null}
const userClient = new KanaUserClient({
  userToken,

  onError: async (err) => {
    console.log(err); // or push errors to a central logger
  },
});
```

If using Typescript, errors will be typed and you can check against this type. The following error types are possible:

* `EmptyArgumentError`

* `FeatureNotFoundError`

* `AuthenticationError`

* `NetworkError`

* `Error `

### Retries

By default, we will retry sending all calls up to 2 times when a `NetworkError` occurs with no backoff or delay. You can override this behaviour with the `retry` argument:

```javascript theme={null}
const userClient = new KanaUserClient({
  userToken,

  retry: (error: Error, retryNumber: number) => {
    return error instanceof NetworkError && retryNumber < 3;
  },
});
```

## Methods

### canUseFeature(featureId, delta?)

Understand if a [User](/reference/admin-api-backend-reference/objects#user) is able to use a particular [Feature](/reference/admin-api-backend-reference/objects#feature).

The returned `access` boolean is `true` when the user has access (for Binary features), has enough of a feature remaining to be used (for Consumable features), or has overage enabled (for Consumable features).

#### Arguments

| Field       | Type                                                             | Text                                                                                                                                       |
| ----------- | ---------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------ |
| `featureId` | [String!](/reference/admin-api-backend-reference/scalars#string) | The id of the feature. This maps to the `id` field as set on the [Feature](/reference/admin-api-backend-reference/objects#feature) object. |
| `delta`     | [Int](/reference/admin-api-backend-reference/scalars#int)        | The amount of the consumable feature which the user will be using and you want to check access against. Defaults to `1`.                   |

#### Returns

A `Promise` that resolves to a [CanUseFeatureData](/reference/admin-api-backend-reference/objects#canusefeaturedata) object.

#### Example

```javascript JS theme={null}
// Initializing the client
import { KanaUserClient } from "@usekana/client-kana-js";

const userToken = "<INSERT_USER_TOKEN_HERE>";
const kanaClient = new KanaUserClient({ userToken });

// Using the method
const { data, error } = await kanaClient.canUseFeature("messages", 1);
console.log(data);
console.log(error);
```

### getSubscribedFeatures()

Lists the [Feature](/reference/admin-api-backend-reference/objects#feature)**s** which a [User](/reference/admin-api-backend-reference/objects#user) has access to.

#### Returns

A `Promise` that resolves to an array of [Feature](/reference/admin-api-backend-reference/objects#feature) objects with only the following fields present:

* `id`

* `name`

* `type`

* `unitLabel`

* `unitLabelPlural`

* `metadata`

#### Example

```javascript theme={null}
// Initializing the client

import { KanaUserClient } from "@usekana/client-kana-js";

const userToken = "<INSERT_USER_TOKEN_HERE>";

const kanaClient = new KanaUserClient({ userToken });

// Using the method

const { data, error } = await kanaClient.getSubscribedFeatures();

console.log(data);

console.log(error);
```

### getSubscribedPackages()

Lists the plans which a user is subscribed to.

#### Returns

A `Promise` that resolves to an array of [Package](/reference/admin-api-backend-reference/objects#package) objects with only the following fields present:

* `id`

* `name`

* `isAddon`

* `metadata`

#### Example

```javascript theme={null}
// Initializing the client

import { KanaUserClient } from "@usekana/client-kana-js";

const userToken = "<INSERT_USER_TOKEN_HERE>";
const kanaClient = new KanaUserClient({ userToken });

// Using the method
const { data, error } = await kanaClient.getSubscribedPackages();
console.log(data);
console.log(error);
```

### resetCache()

Resets a user's data which has been stored in the cache.

By default, the SDK uses the cache to store a user's subscribed packages and features upon initially calling any method. This cached data will then be returned when calling any method subsequently. You will need to call `resetCache()` in order to refresh this data.

#### Returns

A `Promise` that resolves to an empty object if the cache has been successfully reset.

#### Examples

```javascript theme={null}
// Initializing the client

import { KanaUserClient } from "@usekana/client-kana-js";

const userToken = "<INSERT_USER_TOKEN_HERE>";
const kanaClient = new KanaUserClient({ userToken });

// Using the method
await kanaClient.resetCache();
```