All core concepts from the Rate Limiting Guide apply to async rate limiting as well.
You can usually just use the normal synchronous rate limiter and it will work with async functions, but for advanced use cases, such as wanting to use the return value of a rate-limited function (instead of just calling a setState side effect), or putting your error handling logic in the rate limiter, you can use the async rate limiter.
TanStack Pacer provides async rate limiting through the AsyncRateLimiter class and the asyncRateLimit function.
Here's a basic example showing how to use the async rate limiter for an API operation:
const rateLimitedApi = asyncRateLimit(
async (id: string) => {
const response = await fetch(`/api/data/${id}`)
return response.json()
},
{
limit: 5,
window: 1000,
onExecute: (limiter) => {
console.log('API call succeeded:', limiter.store.state.successCount)
},
onReject: (limiter) => {
console.log(`Rate limit exceeded. Try again in ${limiter.getMsUntilNextWindow()}ms`)
},
onError: (error, limiter) => {
console.error('API call failed:', error)
}
}
)
// Usage
try {
const result = await rateLimitedApi('123')
// Handle successful result
} catch (error) {
// Handle errors if no onError handler was provided
console.error('API call failed:', error)
}
const rateLimitedApi = asyncRateLimit(
async (id: string) => {
const response = await fetch(`/api/data/${id}`)
return response.json()
},
{
limit: 5,
window: 1000,
onExecute: (limiter) => {
console.log('API call succeeded:', limiter.store.state.successCount)
},
onReject: (limiter) => {
console.log(`Rate limit exceeded. Try again in ${limiter.getMsUntilNextWindow()}ms`)
},
onError: (error, limiter) => {
console.error('API call failed:', error)
}
}
)
// Usage
try {
const result = await rateLimitedApi('123')
// Handle successful result
} catch (error) {
// Handle errors if no onError handler was provided
console.error('API call failed:', error)
}
Unlike the synchronous rate limiter which returns a boolean indicating success, the async version allows you to capture and use the return value from your rate-limited function. The maybeExecute method returns a Promise that resolves with the function's return value, allowing you to await the result and handle it appropriately.
The async rate limiter provides robust error handling capabilities:
The AsyncRateLimiter supports the following callbacks:
Both the Async and Synchronous rate limiters support the onReject callback for handling blocked executions.
Example:
const asyncLimiter = new AsyncRateLimiter(async (id) => {
await saveToAPI(id)
}, {
limit: 5,
window: 1000,
onExecute: (rateLimiter) => {
// Called after each successful execution
console.log('Async function executed', rateLimiter.store.state.successCount)
},
onReject: (rateLimiter) => {
// Called when an execution is rejected
console.log(`Rate limit exceeded. Try again in ${rateLimiter.getMsUntilNextWindow()}ms`)
},
onError: (error) => {
// Called if the async function throws an error
console.error('Async function failed:', error)
}
})
const asyncLimiter = new AsyncRateLimiter(async (id) => {
await saveToAPI(id)
}, {
limit: 5,
window: 1000,
onExecute: (rateLimiter) => {
// Called after each successful execution
console.log('Async function executed', rateLimiter.store.state.successCount)
},
onReject: (rateLimiter) => {
// Called when an execution is rejected
console.log(`Rate limit exceeded. Try again in ${rateLimiter.getMsUntilNextWindow()}ms`)
},
onError: (error) => {
// Called if the async function throws an error
console.error('Async function failed:', error)
}
})
Since the rate limiter's maybeExecute method returns a Promise, you can choose to await each execution before starting the next one. This gives you control over the execution order and ensures each call processes the most up-to-date data. This is particularly useful when dealing with operations that depend on the results of previous calls or when maintaining data consistency is critical.
For example, if you're updating a user's profile and then immediately fetching their updated data, you can await the update operation before starting the fetch.
Just like the synchronous rate limiter, the async rate limiter supports dynamic options for limit, window, and enabled, which can be functions that receive the rate limiter instance. This allows for sophisticated, runtime-adaptive rate limiting behavior.
Each framework adapter provides hooks that build on top of the core async rate limiting functionality to integrate with the framework's state management system. Hooks like createAsyncRateLimiter, useAsyncRateLimitedCallback, or similar are available for each framework.
The AsyncRateLimiter class uses TanStack Store for reactive state management, providing real-time access to execution state, error tracking, and rejection statistics.
When using the AsyncRateLimiter class directly, access state via the store.state property:
const asyncLimiter = new AsyncRateLimiter(asyncFn, { limit: 5, window: 1000 })
// Access current state
console.log(asyncLimiter.store.state.isExecuting)
const asyncLimiter = new AsyncRateLimiter(asyncFn, { limit: 5, window: 1000 })
// Access current state
console.log(asyncLimiter.store.state.isExecuting)
When using framework adapters like React or Solid, the state is exposed directly as a reactive property:
// React example
const asyncLimiter = useAsyncRateLimiter(asyncFn, { limit: 5, window: 1000 })
// Access state directly (reactive)
console.log(asyncLimiter.state.successCount) // Reactive value
console.log(asyncLimiter.state.isExecuting) // Reactive value
// React example
const asyncLimiter = useAsyncRateLimiter(asyncFn, { limit: 5, window: 1000 })
// Access state directly (reactive)
console.log(asyncLimiter.state.successCount) // Reactive value
console.log(asyncLimiter.state.isExecuting) // Reactive value
You can provide initial state values when creating an async rate limiter:
const asyncLimiter = new AsyncRateLimiter(asyncFn, {
limit: 5,
window: 1000,
initialState: {
successCount: 3, // Start with 3 successful executions
errorCount: 1, // Start with 1 error
rejectionCount: 2, // Start with 2 rejections
lastResult: 'initial-result', // Start with initial result
executionTimes: [Date.now() - 500], // Start with one execution timestamp
}
})
const asyncLimiter = new AsyncRateLimiter(asyncFn, {
limit: 5,
window: 1000,
initialState: {
successCount: 3, // Start with 3 successful executions
errorCount: 1, // Start with 1 error
rejectionCount: 2, // Start with 2 rejections
lastResult: 'initial-result', // Start with initial result
executionTimes: [Date.now() - 500], // Start with one execution timestamp
}
})
The store is reactive and supports subscriptions:
const asyncLimiter = new AsyncRateLimiter(asyncFn, { limit: 5, window: 1000 })
// Subscribe to state changes
const unsubscribe = asyncLimiter.store.subscribe((state) => {
console.log('Success count:', state.successCount)
console.log('Error count:', state.errorCount)
console.log('Rejection count:', state.rejectionCount)
console.log('Currently executing:', state.isExecuting)
})
// Unsubscribe when done
unsubscribe()
const asyncLimiter = new AsyncRateLimiter(asyncFn, { limit: 5, window: 1000 })
// Subscribe to state changes
const unsubscribe = asyncLimiter.store.subscribe((state) => {
console.log('Success count:', state.successCount)
console.log('Error count:', state.errorCount)
console.log('Rejection count:', state.rejectionCount)
console.log('Currently executing:', state.isExecuting)
})
// Unsubscribe when done
unsubscribe()
The AsyncRateLimiterState includes:
The async rate limiter provides helper methods that compute values based on the current state:
const asyncLimiter = new AsyncRateLimiter(asyncFn, { limit: 5, window: 1000 })
// These methods use the current state to compute values
console.log(asyncLimiter.getRemainingInWindow()) // Number of calls remaining in current window
console.log(asyncLimiter.getMsUntilNextWindow()) // Milliseconds until next window
const asyncLimiter = new AsyncRateLimiter(asyncFn, { limit: 5, window: 1000 })
// These methods use the current state to compute values
console.log(asyncLimiter.getRemainingInWindow()) // Number of calls remaining in current window
console.log(asyncLimiter.getMsUntilNextWindow()) // Milliseconds until next window
These methods are computed values that use the current state and don't need to be accessed through the store.
For core rate limiting concepts and synchronous rate limiting, see the Rate Limiting Guide.
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