Defined in: async-rate-limiter.ts:187

A class that creates an async 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.

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.

Unlike the non-async RateLimiter, this async version supports returning values from the rate-limited function, making it ideal for API calls and other async operations where you want the result of the maybeExecute call instead of setting the result on a state variable from within the rate-limited function.

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
• initialState can be a partial state object
• Use onSuccess callback to react to successful function execution and implement custom logic
• Use onError callback to react to function execution errors and implement custom error handling
• Use onSettled callback to react to function execution completion (success or error) and implement custom logic
• Use onReject callback to react to executions being rejected when rate limit is exceeded
• The state includes execution times, success/error counts, and current execution status
• State can be accessed via asyncRateLimiter.store.state when using the class directly
• When using framework adapters (React/Solid), state is accessed from asyncRateLimiter.state

Error Handling:

• If an onError handler is provided, it will be called with the error and rate limiter instance
• If throwOnError is true (default when no onError handler is provided), the error will be thrown
• If throwOnError is false (default when onError handler is provided), the error will be swallowed
• Both onError and throwOnError can be used together - the handler will be called before any error is thrown
• The error state can be checked using the underlying AsyncRateLimiter instance
• Rate limit rejections (when limit is exceeded) are handled separately from execution errors via the onReject handler

const rateLimiter = new AsyncRateLimiter(
  async (id: string) => await api.getData(id),
  {
    limit: 5,
    window: 1000,
    windowType: 'sliding',
    onError: (error) => {
      console.error('API call failed:', error);
    },
    onReject: (limiter) => {
      console.log(`Rate limit exceeded. Try again in ${limiter.getMsUntilNextWindow()}ms`);
    }
  }
);

// Will execute immediately until limit reached, then block
// Returns the API response directly
const data = await rateLimiter.maybeExecute('123');

const rateLimiter = new AsyncRateLimiter(
  async (id: string) => await api.getData(id),
  {
    limit: 5,
    window: 1000,
    windowType: 'sliding',
    onError: (error) => {
      console.error('API call failed:', error);
    },
    onReject: (limiter) => {
      console.log(`Rate limit exceeded. Try again in ${limiter.getMsUntilNextWindow()}ms`);
    }
  }
);

// Will execute immediately until limit reached, then block
// Returns the API response directly
const data = await rateLimiter.maybeExecute('123');

• TFn extends AnyAsyncFunction

new AsyncRateLimiter<TFn>(fn, initialOptions): AsyncRateLimiter<TFn>

new AsyncRateLimiter<TFn>(fn, initialOptions): AsyncRateLimiter<TFn>

Defined in: async-rate-limiter.ts:193

TFn

AsyncRateLimiterOptions<TFn>

AsyncRateLimiter<TFn>

options: AsyncRateLimiterOptions<TFn>;

options: AsyncRateLimiterOptions<TFn>;

Defined in: async-rate-limiter.ts:191

readonly store: Store<Readonly<AsyncRateLimiterState<TFn>>>;

readonly store: Store<Readonly<AsyncRateLimiterState<TFn>>>;

Defined in: async-rate-limiter.ts:188

getMsUntilNextWindow(): number

getMsUntilNextWindow(): number

Defined in: async-rate-limiter.ts:366

Returns the number of milliseconds until the next execution will be possible For fixed windows, this is the time until the current window resets For sliding windows, this is the time until the oldest execution expires

number

getRemainingInWindow(): number

getRemainingInWindow(): number

Defined in: async-rate-limiter.ts:356

Returns the number of remaining executions allowed in the current window

number

maybeExecute(...args): Promise<undefined | ReturnType<TFn>>

maybeExecute(...args): Promise<undefined | ReturnType<TFn>>

Defined in: async-rate-limiter.ts:268

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.

Error Handling:

• If the rate-limited function throws and no onError handler is configured, the error will be thrown from this method.
• If an onError handler is configured, errors will be caught and passed to the handler, and this method will return undefined.
• The error state can be checked using getErrorCount() and getIsExecuting().

...Parameters<TFn>

Promise<undefined | ReturnType<TFn>>

A promise that resolves with the function's return value, or undefined if an error occurred and was handled by onError

The error from the rate-limited function if no onError handler is configured

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

// First 5 calls will return a promise that resolves with the result
const result = await rateLimiter.maybeExecute('arg1', 'arg2');

// Additional calls within the window will return undefined
const result2 = await rateLimiter.maybeExecute('arg1', 'arg2'); // undefined

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

// First 5 calls will return a promise that resolves with the result
const result = await rateLimiter.maybeExecute('arg1', 'arg2');

// Additional calls within the window will return undefined
const result2 = await rateLimiter.maybeExecute('arg1', 'arg2'); // undefined

reset(): void

reset(): void

Defined in: async-rate-limiter.ts:377

Resets the rate limiter state

void

setOptions(newOptions): void

setOptions(newOptions): void

Defined in: async-rate-limiter.ts:208

Updates the async rate limiter options

Partial<AsyncRateLimiterOptions<TFn>>

void