---
sidebar_position: 4
title: Cache
sidebar_label: Cache
---

<div class="api-link">
  <div class="api-link-title">Cache</div>
  <div class="api-link-sub-title">

[Read the API Reference »](/api/Hyper-Fetch/Class/Cache.mdx)

  </div>
</div>

---

## Introduction

**`Cache`** stores response data from requests. It uses an event system that successively transmits data and takes care
of validation in the system. Data is stored under `cacheKey` in the storage (which by default is a Map object, but can
be replaced by any other compatible interface).

---

## Purpose

- Stores request results
- Manages stored data
- Emits storage events

---

## CacheKey

The cache stores data on a `key-value` basis. The key is always specified inside the request as `cacheKey`; it
determines where the data is stored and is used in propagation of data handling events.

By default, the cacheKey value is auto-determined based on the **method**, **endpoint**, and **query params** of the
given request. However, there is nothing to prevent you manually adding the key when setting the request or using one of
its methods.

Thanks to the automatic way of indexing data in the cache, we do not have to worry about paginated keys in the data –
everything will happen automatically.

---

## Events

Available cache events.

{@import Hyper-Fetch getCacheEvents returns}

---

## Storage

By default, the cache uses Map as a data retention location. However, you can also choose where the data is stored in
the system – i.e. local storage or IndexedDB – regardless if the source works synchronously or asynchronously. This
allows you to set up persistent storage across sessions.

```tsx
export const client = new Client<ServerErrorType>({
  url: "localhost:3000",
  cache: (instance) =>
    new Cache(instance, {
      storage,
    }),
});
```

---

## Read Cache

The cache can be read using the `get` method. It returns the data stored under the given key.

```tsx
const data = client.cache.get("key");

// OR

const getUsers = client.createRequest()({
  method: "GET",
  endpoint: "/users",
});
const data = client.cache.get(getUsers.cacheKey);

// OR

const getUsers = client.createRequest()({
  method: "GET",
  endpoint: "/users",
  cacheKey: "CUSTOM_CACHE_KEY",
});
const data = client.cache.get("CUSTOM_CACHE_KEY");
const data = client.cache.get(getUsers.cacheKey);

// OR Dynamic

const getNote = client.createRequest()({
  method: "GET",
  endpoint: "/notes/:noteId",
});
const data = client.cache.get(getNote.setParams({ noteId: 1 }).cacheKey);
```

---

## Write Cache

The cache can be written using the `set` method. It stores the data under the given key. We MUST pass the whole request
to the set method as it stores configuration related to cache time, garbage colletion, etc.

`You can set everything you want, error states, extra data, etc.` The cache will take care of the rest and will emit all
necessary events. This way our subsystems will receive it and will be able to react to it.

```tsx
const getNote = client.createRequest()({
  method: "GET",
  endpoint: "/notes/:noteId",
});

client.cache.set(getNote.setParams({ noteId: 1 }), {
  data: { text: "Hello World" },
  error: null,
  status: 200,
  success: true,
  extra: xhrExtra,
});

// You can also use callback to read previous data

client.cache.set(getNote.setParams({ noteId: 1 }), (prevData) => ({
  ...prevData,
  data: { text: "Hello World" },
}));
```

---

## Update Cache

We can update cache by using the `update` method. It updates the data under the given key. We pass the whole request to
method in similar way as we did it with `set` method.

:::info

Cache will be **NOT** updated if the initial data is not present in the cache.

:::

```tsx
const getNote = client.createRequest()({
  method: "GET",
  endpoint: "/notes/:noteId",
});

client.cache.update(getNote.setParams({ noteId: 1 }), {
  data: { text: "Hello World" },
  error: null,
  status: 200,
  success: true,
  extra: xhrExtra,
});

// You can also use callback to read previous data

client.cache.update(getNote.setParams({ noteId: 1 }), (prevData) => ({
  ...prevData,
  data: { text: "Hello World" },
}));
```

---

## Delete Cache

To delete data from the cache, we can use the `delete` method. It deletes the data under the given key.

```tsx
const getNote = client.createRequest()({
  method: "GET",
  endpoint: "/notes/:noteId",
});

client.cache.delete(getNote.setParams({ noteId: 1 }).cacheKey);

// OR

client.cache.delete("CUSTOM_CACHE_KEY");
```

---

## Invalidate Cache

You can also invalidate the cache by using the `invalidate` method. It deletes the data under the given key and emits
event, so **in case of using it with for example React, it will refetch the data**.

```tsx
const getNote = client.createRequest()({
  method: "GET",
  endpoint: "/notes/:noteId",
});

client.cache.invalidate(getNote.setParams({ noteId: 1 }).cacheKey);

// OR

client.cache.invalidate("CUSTOM_CACHE_KEY");

// OR via RegExp

client.cache.invalidate(new RegExp("CUSTOM_CACHE_KEY"));
```

---

## Persistence

We can achieve the persistence of stored data by changing the cache storage to persistent. It must match the provided
interface.

#### [Read More](/guides/02-advanced/persistence.mdx)

:::info

Currently there is no cross-tab synchronization. It's planned for a future release.

:::

---

## Lifecycle

Cache options can be provided with some lifecycle methods. These are events such as `onInitialization`.

---

## Parameters

Configuration options

{@import Hyper-Fetch CacheOptionsType returns}
