---
title: 'Creating a Store'
icon: 'database'
---

### Overview

A store tracks how many hits each client (identified via their IP address) has
received and automatically reduce that hit count as time elapses.

### The `Store` Interface

A store **must** have the `increment`, `decrement`, and `resetKey` public
methods. It may optionally have the `init`, `get` and `resetAll` public methods
and a `prefix` (string) or `localKeys` (boolean) field. For backwards
compatibility with versions prior to `6.0.0`, it may also have the `incr` and
`decr` public methods. Finally, it may have a `constructor` and any number of
private methods.

The `increment` method is the primary interface between the middleware and the
store. It adds 1 to the internal count for a key and returns an object
consisting of the new internal count (`totalHits`) and the time that the count
will reach 0 (`resetTime`).

The `decrement` method is used only to 'uncount' requests when one or both of
the `skipSuccessfulRequests` or `skipFailedRequests` options are enabled.

The `init` method allows the store to set itself up using the options passed to
the middleware. The store can get the `windowMs` option from this method.

<Note>

    Starting with version 8.5.0, the `init` method may be async, and is a good place
    for things like opening a connection to a database or ensuring the schema is
    up-to-date. Errors & promise rejections from `init` will be caught and logged by
    express-rate-limit, but will not prevent other methods such as `increment()`
    from being called. Additionally, other methods such as `increment()` may be
    called before `init()` completes.

</Note>

The `get` method takes a `string` argument (the key that identifies a client)
and returns an object consisting of the internal hit count (`totalHits`) and the
time that the count will reach 0 (`resetTime`) for the given client. It may
return `undefined` if it cannot find the key.

The `resetKey` method takes a `string` argument (the key that identifies a
client) and sets the internal count for that key to zero.

The `resetAll` method takes no arguments and sets the internal count for all
keys to zero.

The `prefix` field is used to avoid conflicts when the user creates multiple
instances of the store for multiple rate limits (e.g. 10 hits per minute and 60
hits per hour). Keys in the database should be prefixed with this value.
`prefix` is generally passed as an option to the constructor. (The `singleCount`
validation check also takes the `prefix` field into account and does not report
that a user is being double-counted if the stores have different prefixes.)

The `localKeys` field is an alternative to `prefix` for stores such as the
MemoryStore where two instances will automatically keep separate counts. Setting
it to `true` will prevent false positives from the `singleCount` validation
check.

The `get` and `resetKey` methods can be called from the middleware, like so:

```ts
// Create a rate limiter.
const limiter = rateLimit({/* ... */})

// Fetch or reset the hit count for a key.
limiter.get('1.2.3.4')
limiter.resetKey('1.2.3.4')
```

### Dependency configuration

Add `express-rate-limit` as a peer dependency, and a development dependency to
the package:

```json package.json
{
	"peerDependencies": {
		"express-rate-limit": ">= 6"
	},
	"devDependencies": {
		"express-rate-limit": "*"
	}
}
```

<Note>

    If the store supports the `incr` method, replace `>= 6` with `>= 2.3.0`

</Note>

### Example Typescript and Javascript Stores

<CodeGroup>

```ts typescript-store.ts
import type {
	Store,
	Options,
	IncrementResponse,
	ClientRateLimitInfo,
} from 'express-rate-limit'

type SomeStoreOptions = {
	/**
	 * Optional field to differentiate hit countswhen multiple rate-limits are in use
	 */
	prefix?: string

	/**
	 * Some store-specific parameter
	 */
	customParam: string
}

/**
 * A `Store` that stores the hit count for each client.
 *
 * @public
 */
class SomeStore implements Store {
	/**
	 * Some store-specific parameter.
	 */
	customParam!: string

	/**
	 * The duration of time before which all hit counts are reset (in milliseconds).
	 */
	windowMs!: number

	prefix!: string

	/**
	 * @constructor for `SomeStore`. Only required if the user needs to pass
	 * some store specific parameters. For example, in a Mongo Store, the user will
	 * need to pass the URI, username and password for the Mongo database.
	 *
	 * Accepting a custom `prefix` here is also recommended.
	 *
	 * @param options {SomeStoreOptions} - Prefix and any store-specific parameters.
	 */
	constructor(options: SomeStoreOptions) {
		this.customParam = options.customParam
		this.prefix = options.prefix ?? 'rl_'
	}

	/**
	 * Method that actually initializes the store.
	 *
	 * This method is optional, it will be called only if it exists.
	 *
	 * @param options {Options} - The options used to setup express-rate-limit.
	 *
	 * @public
	 */
	async init(options: Options): Promise<void> {
		this.windowMs = options.windowMs
		// ...
	}

	/**
	 * Method to prefix the keys with the given text.
	 *
	 * Call this from get, increment, decrement, resetKey, etc.
	 *
	 * @param key {string} - The key.
	 *
	 * @returns {string} - The text + the key.
	 */
	prefixKey(key: string): string {
		return `${this.prefix}${key}`
	}

	/**
	 * Method to fetch a client's hit count and reset time.
	 *
	 * @param key {string} - The identifier for a client.
	 *
	 * @returns {ClientRateLimitInfo} - The number of hits and reset time for that client.
	 *
	 * @public
	 */
	async get(key: string): Promise<ClientRateLimitInfo | undefined> {
		// ...
		return {
			totalHits,
			resetTime,
		}
	}

	/**
	 * Method to increment a client's hit counter.
	 *
	 * @param key {string} - The identifier for a client.
	 *
	 * @returns {IncrementResponse} - The number of hits and reset time for that client.
	 *
	 * @public
	 */
	async increment(key: string): Promise<IncrementResponse> {
		// ...
		return {
			totalHits,
			resetTime,
		}
	}

	/**
	 * Method to decrement a client's hit counter.
	 *
	 * @param key {string} - The identifier for a client.
	 *
	 * @public
	 */
	async decrement(key: string): Promise<void> {
		// ...
	}

	/**
	 * Method to reset a client's hit counter.
	 *
	 * @param key {string} - The identifier for a client.
	 *
	 * @public
	 */
	async resetKey(key: string): Promise<void> {
		// ...
	}

	/**
	 * Method to reset everyone's hit counter.
	 *
	 * This method is optional, it is never called by express-rate-limit.
	 *
	 * @public
	 */
	async resetAll(): Promise<void> {
		// ...
	}
}

// Export the store so others can use it
export default SomeStore
```

```js javascript-store.js
/**
 * A `Store` that stores the hit count for each client.
 *
 * @public
 */
class SomeStore {
	/**
	 * @constructor for `SomeStore`. Only required if the user needs to pass
	 * some store specific parameters. For example, in a Mongo Store, the user will
	 * need to pass the URI, username and password for the Mongo database.
	 *
	 * Accepting a custom `prefix` here is also recommended.
	 *
	 * @param options {SomeStoreOptions} - Prefix and any store-specific parameters.
	 */
	constructor({ customParam, prefix }) {
		this.customParam = options.customParam
		this.prefix = options.prefix ?? 'rl_'
	}

	/**
	 * Method that actually initializes the store.
	 *
	 * This method is optional, it will be called only if it exists.
	 *
	 * @param options {Options} - The options used to setup express-rate-limit.
	 *
	 * @public
	 */
	async init(options) {
		this.windowMs = options.windowMs
	}

	/**
	 * Method to prefix the keys with the given text.
	 *
	 * Call this from get, increment, decrement, resetKey, etc.
	 *
	 * @param key {string} - The key.
	 *
	 * @returns {string} - The text + the key.
	 */
	prefixKey(key) {
		return `${this.prefix}${key}`
	}

	/**
	 * Method to fetch a client's hit count and reset time.
	 *
	 * @param key {string} - The identifier for a client.
	 *
	 * @returns {ClientRateLimitInfo} - The number of hits and reset time for that client.
	 *
	 * @public
	 */
	async get(key) {
		// ...
		return {
			totalHits,
			resetTime,
		}
	}

	/**
	 * Method to increment a client's hit counter.
	 *
	 * @param key {string} - The identifier for a client.
	 *
	 * @returns {IncrementResponse} - The number of hits and reset time for that client.
	 *
	 * @public
	 */
	async increment(key) {
		// ...

		return {
			totalHits, // A positive integer
			resetTime, // A JS `Date` object
		}
	}

	/**
	 * Method to decrement a client's hit counter.
	 *
	 * @param key {string} - The identifier for a client.
	 *
	 * @public
	 */
	async decrement(key) {
		// ...
	}

	/**
	 * Method to reset a client's hit counter.
	 *
	 * @param key {string} - The identifier for a client.
	 *
	 * @public
	 */
	async resetKey(key) {
		// ...
	}

	/**
	 * Method to reset everyone's hit counter.
	 *
	 * This method is optional, it is never called by express-rate-limit.
	 *
	 * @public
	 */
	async resetAll() {
		// ...
	}
}

// Export the store so others can use it
// ...via the CommonJS style
module.exports = SomeStore
// ...or the ES Module style
export default SomeStore
```

</CodeGroup>

### Using a Custom Store

```ts
// Use `const { rateLimit } = require('...')` instead if you are using CommonJS
import { rateLimit } from 'express-rate-limit'
import SomeStore from './some-store.js'

const limiter = rateLimit({
	store: new SomeStore({ customParam: '🎉' }),
})
```
