Class: AsyncRateLimiter\

A class that creates an async rate-limited function.

Async vs Sync Versions: The async version provides advanced features over the sync RateLimiter:

Returns promises that can be awaited for rate-limited function results
Built-in retry support via AsyncRetryer integration
Abort support to cancel in-flight executions
Comprehensive error handling with onError callbacks and throwOnError control
Detailed execution tracking (success/error/settle counts, rejection counts)
More sophisticated window management with automatic cleanup
The sync RateLimiter is lighter weight and simpler when you don't need async features, return values, or execution control.
What is Rate Limiting? Rate limiting 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.
Window Types:
'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.
When to Use Rate Limiting: 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.
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)
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

Example

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');

Type Parameters

TFn

TFn extends AnyAsyncFunction

Constructors

Constructor

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

Defined in: async-rate-limiter.ts:254

Parameters

initialOptions

AsyncRateLimiterOptions\<`TFn`\>

Returns

AsyncRateLimiter\<`TFn`\>

Properties

asyncRetryers

asyncRetryers: Map<number, AsyncRetryer<TFn>>;

Defined in: async-rate-limiter.ts:251

key

key: string | undefined;

Defined in: async-rate-limiter.ts:249

options

options: AsyncRateLimiterOptions<TFn>;

Defined in: async-rate-limiter.ts:250

store

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

Defined in: async-rate-limiter.ts:246

Methods

abort()

abort(): void;

Defined in: async-rate-limiter.ts:539

Aborts all ongoing executions with the internal abort controllers. Does NOT clear out the execution times or reset the rate limiter.

Returns

void

getAbortSignal()

getAbortSignal(maybeExecuteCount?): AbortSignal | null;

Defined in: async-rate-limiter.ts:529

Returns the AbortSignal for a specific execution. If no maybeExecuteCount is provided, returns the signal for the most recent execution. Returns null if no execution is found or not currently executing.

Parameters

maybeExecuteCount?

number

Optional specific execution to get signal for

Returns

AbortSignal | null

Example

const rateLimiter = new AsyncRateLimiter(
  async (userId: string) => {
    const signal = rateLimiter.getAbortSignal()
    if (signal) {
      const response = await fetch(`/api/users/${userId}`, { signal })
      return response.json()
    }
  },
  { limit: 5, window: 1000 }
)

getMsUntilNextWindow()

getMsUntilNextWindow(): number;

Defined in: async-rate-limiter.ts:501

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

Returns

number

getRemainingInWindow()

getRemainingInWindow(): number;

Defined in: async-rate-limiter.ts:491

Returns the number of remaining executions allowed in the current window

Returns

number

maybeExecute()

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

Defined in: async-rate-limiter.ts:358

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

args

...Parameters\<`TFn`\>

Returns

Promise\<`ReturnType`\<`TFn`\> | undefined>

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

Throws

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

Example

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