asyncRateLimit
Function: asyncRateLimit()
function asyncRateLimit<TFn>(fn, initialOptions): (...args) => Promise<undefined | ReturnType<TFn>>
function asyncRateLimit<TFn>(fn, initialOptions): (...args) => Promise<undefined | ReturnType<TFn>>
Defined in: async-rate-limiter.ts:322
Creates an async rate-limited function that will execute the provided function up to a maximum number of times within a time window.
Unlike the non-async rate limiter, 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.
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.
Note that rate limiting is a simpler form of execution control compared to throttling or debouncing:
- A rate limiter will allow all executions until the limit is reached, then block all subsequent calls until the window resets
- A throttler ensures even spacing between executions, which can be better for consistent performance
- A debouncer collapses multiple calls into one, which is better for handling bursts of events
Consider using throttle() or debounce() if you need more intelligent execution control. Use rate limiting when you specifically need to enforce a hard limit on the number of executions within a time period.
Type Parameters
• TFn extends AnyAsyncFunction
Parameters
fn
TFn
initialOptions
Omit<AsyncRateLimiterOptions<TFn>, "enabled">
Returns
Function
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. If execution is allowed, waits for any previous execution to complete before proceeding.
Parameters
args
...Parameters<TFn>
Returns
Promise<undefined | ReturnType<TFn>>
Example
const rateLimiter = new AsyncRateLimiter(fn, { limit: 5, window: 1000 });
// First 5 calls will execute
await rateLimiter.maybeExecute('arg1', 'arg2');
// Additional calls within the window will be rejected
await rateLimiter.maybeExecute('arg1', 'arg2'); // Rejected
const rateLimiter = new AsyncRateLimiter(fn, { limit: 5, window: 1000 });
// First 5 calls will execute
await rateLimiter.maybeExecute('arg1', 'arg2');
// Additional calls within the window will be rejected
await rateLimiter.maybeExecute('arg1', 'arg2'); // Rejected
Example
// Rate limit to 5 calls per minute with a sliding window
const rateLimited = asyncRateLimit(makeApiCall, {
limit: 5,
window: 60000,
windowType: 'sliding',
onReject: (rateLimiter) => {
console.log(`Rate limit exceeded. Try again in ${rateLimiter.getMsUntilNextWindow()}ms`);
}
});
// First 5 calls will execute immediately
// Additional calls will be rejected until the minute window resets
// Returns the API response directly
const result = await rateLimited();
// For more even execution, consider using throttle instead:
const throttled = throttle(makeApiCall, { wait: 12000 }); // One call every 12 seconds
// Rate limit to 5 calls per minute with a sliding window
const rateLimited = asyncRateLimit(makeApiCall, {
limit: 5,
window: 60000,
windowType: 'sliding',
onReject: (rateLimiter) => {
console.log(`Rate limit exceeded. Try again in ${rateLimiter.getMsUntilNextWindow()}ms`);
}
});
// First 5 calls will execute immediately
// Additional calls will be rejected until the minute window resets
// Returns the API response directly
const result = await rateLimited();
// For more even execution, consider using throttle instead:
const throttled = throttle(makeApiCall, { wait: 12000 }); // One call every 12 seconds
Subscribe to Bytes
Your weekly dose of JavaScript news. Delivered every Monday to over 100,000 devs, for free.