# createAsyncThrottler

# Function: createAsyncThrottler()

```ts
function createAsyncThrottler<TFn, TSelected>(
   fn, 
   options, 
selector): SolidAsyncThrottler<TFn, TSelected>;
```

Defined in: [solid-pacer/src/async-throttler/createAsyncThrottler.ts:175](https://github.com/TanStack/pacer/blob/main/packages/solid-pacer/src/async-throttler/createAsyncThrottler.ts#L175)

A low-level Solid hook that creates an `AsyncThrottler` instance to limit how often an async function can execute.

This hook is designed to be flexible and state-management agnostic - it simply returns a throttler instance that
you can integrate with any state management solution (createSignal, etc).

Async throttling ensures an async function executes at most once within a specified time window,
regardless of how many times it is called. This is useful for rate-limiting expensive API calls,
database operations, or other async tasks.

Unlike the non-async Throttler, this async version supports returning values from the throttled 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 throttled function.

Error Handling:
- If an `onError` handler is provided, it will be called with the error and throttler 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 AsyncThrottler instance

## State Management and Selector

The hook uses TanStack Store for reactive state management. You can subscribe to state changes
in two ways:

**1. Using `throttler.Subscribe` component (Recommended for component tree subscriptions)**

Use the `Subscribe` component to subscribe to state changes deep in your component tree without
needing to pass a selector to the hook. This is ideal when you want to subscribe to state
in child components.

**2. Using the `selector` parameter (For hook-level subscriptions)**

The `selector` parameter allows you to specify which state changes will trigger reactive updates
at the hook level, optimizing performance by preventing unnecessary updates when irrelevant
state changes occur.

**By default, there will be no reactive state subscriptions** and you must opt-in to state
tracking by providing a selector function or using the `Subscribe` component. This prevents unnecessary
updates and gives you full control over when your component tracks state changes.

Available state properties:
- `canLeadingExecute`: Whether the throttler can execute on the leading edge
- `canTrailingExecute`: Whether the throttler can execute on the trailing edge
- `executionCount`: Number of function executions that have been completed
- `hasError`: Whether the last execution resulted in an error
- `isPending`: Whether the throttler is waiting for the timeout to trigger execution
- `isExecuting`: Whether an async function execution is currently in progress
- `lastArgs`: The arguments from the most recent call to maybeExecute
- `lastError`: The error from the most recent failed execution (if any)
- `lastExecutionTime`: Timestamp of the last execution
- `lastResult`: The result from the most recent successful execution
- `nextExecutionTime`: Timestamp of the next allowed execution
- `status`: Current execution status ('disabled' | 'idle' | 'pending' | 'executing')

## Unmount behavior

By default, the primitive cancels any pending execution and aborts any in-flight execution when the owning component unmounts.
Abort only cancels underlying operations (e.g. fetch) when the abort signal from `getAbortSignal()` is passed to them.
Use the `onUnmount` option to customize this. For example, to flush pending work instead:

```tsx
const throttler = createAsyncThrottler(fn, {
  wait: 1000,
  onUnmount: (t) => t.flush()
});
```

Note: For async utils, `flush()` returns a Promise and runs fire-and-forget in the cleanup.
If your throttled function updates Solid signals, those updates may run after the component has
unmounted, which can cause unexpected reactive updates. Guard your callbacks accordingly when
using onUnmount with flush.

## Type Parameters

### TFn

`TFn` *extends* `AnyAsyncFunction`

### TSelected

`TSelected` = \{
\}

## Parameters

### fn

`TFn`

### options

[`SolidAsyncThrottlerOptions`](../interfaces/SolidAsyncThrottlerOptions.md)\<`TFn`, `TSelected`\>

### selector

(`state`) => `TSelected`

## Returns

[`SolidAsyncThrottler`](../interfaces/SolidAsyncThrottler.md)\<`TFn`, `TSelected`\>

## Example

```tsx
// Default behavior - no reactive state subscriptions
const { maybeExecute } = createAsyncThrottler(
  async (id: string) => {
    const data = await api.fetchData(id);
    return data;
  },
  { wait: 1000 }
);

// Opt-in to track isPending or isExecuting changes (optimized for loading states)
const throttler = createAsyncThrottler(
  async (query) => {
    const result = await searchAPI(query);
    return result;
  },
  { wait: 2000 },
  (state) => ({ isPending: state.isPending, isExecuting: state.isExecuting })
);

// Opt-in to track error state changes (optimized for error handling)
const throttler = createAsyncThrottler(
  async (query) => {
    const result = await searchAPI(query);
    return result;
  },
  {
    wait: 2000,
    leading: true,   // Execute immediately on first call
    trailing: false, // Skip trailing edge updates
    onError: (error) => {
      console.error('API call failed:', error);
    }
  },
  (state) => ({ hasError: state.hasError, lastError: state.lastError })
);

// Access the selected state (will be empty object {} unless selector provided)
const { isPending, isExecuting } = throttler.state();
```