RateLimiter

A class that creates a rate-limited function.

Rate limiting is a simple approach that allows a function to execute up to a limit within a time window, then blocks all subsequent calls until the window passes. This can lead to "bursty" behavior where all executions happen immediately, followed by a complete block. This synchronous version is lighter weight and often all you need - upgrade to AsyncRateLimiter when you need promises, retry support, abort capabilities, or advanced error handling.

The rate limiter supports two types of windows:

'fixed': A strict window that resets after the window period. All executions within the window count towards the limit, and the window resets completely after the period.
'sliding': A rolling window that allows executions as old ones expire. This provides a more consistent rate of execution over time.

For smoother execution patterns, consider using:

Throttling: Ensures consistent spacing between executions (e.g. max once per 200ms)
Debouncing: Waits for a pause in calls before executing (e.g. after 500ms of no calls)

Rate limiting is best used for hard API limits or resource constraints. For UI updates or smoothing out frequent events, throttling or debouncing usually provide better user experience.

State Management:

Uses TanStack Store for reactive state management
Use initialState to provide initial state values when creating the rate limiter
Use onExecute callback to react to function execution and implement custom logic
Use onReject callback to react to executions being rejected when rate limit is exceeded
The state includes execution count, execution times, and rejection count
State can be accessed via rateLimiter.store.state when using the class directly
When using framework adapters (React/Solid), state is accessed from rateLimiter.state

Example

const rateLimiter = new RateLimiter(
  (id: string) => api.getData(id),
  {
    limit: 5,
    window: 1000,
    windowType: 'sliding',
  }
);

// Will execute immediately until limit reached, then block
rateLimiter.maybeExecute('123');

Type Parameters

TFn

TFn extends AnyFunction

Constructors

Constructor

new RateLimiter<TFn>(fn, initialOptions): RateLimiter<TFn>;

Defined in: rate-limiter.ts:163

Parameters

fn

TFn

initialOptions

RateLimiterOptions<TFn>

Returns

RateLimiter<TFn>

Properties

fn

fn: TFn;

Defined in: rate-limiter.ts:164

key

key: string | undefined;

Defined in: rate-limiter.ts:159

options

options: RateLimiterOptions<TFn>;

Defined in: rate-limiter.ts:160

store

readonly store: Store<Readonly<RateLimiterState>>;

Defined in: rate-limiter.ts:157

Methods

getMsUntilNextWindow()

getMsUntilNextWindow(): number;

Defined in: rate-limiter.ts:358

Returns the number of milliseconds until the next execution will be possible

Returns

number

getRemainingInWindow()

getRemainingInWindow(): number;

Defined in: rate-limiter.ts:350

Returns the number of remaining executions allowed in the current window

Returns

number

maybeExecute()

maybeExecute(...args): boolean;

Defined in: rate-limiter.ts:252

Attempts to execute the rate-limited function if within the configured limits. Will reject execution if the number of calls in the current window exceeds the limit.

Parameters

args

...Parameters<TFn>

Returns

boolean

Example

const rateLimiter = new RateLimiter(fn, { limit: 5, window: 1000 });

// First 5 calls will return true
rateLimiter.maybeExecute('arg1', 'arg2'); // true

// Additional calls within the window will return false
rateLimiter.maybeExecute('arg1', 'arg2'); // false