# createAsyncBatcher

# Function: createAsyncBatcher()

```ts
function createAsyncBatcher<TValue, TSelected>(
   fn, 
   options, 
selector): SolidAsyncBatcher<TValue, TSelected>;
```

Defined in: [solid-pacer/src/async-batcher/createAsyncBatcher.ts:189](https://github.com/TanStack/pacer/blob/main/packages/solid-pacer/src/async-batcher/createAsyncBatcher.ts#L189)

Creates a Solid-compatible AsyncBatcher instance for managing asynchronous batches of items, exposing Solid signals for all stateful properties.

This is the async version of the createBatcher hook. Unlike the sync version, this async batcher:
- Handles promises and returns results from batch executions
- Provides error handling with configurable error behavior
- Tracks success, error, and settle counts separately
- Has state tracking for when batches are executing
- Returns the result of the batch function execution

Features:
- Configurable batch size and wait time
- Custom batch processing logic via getShouldExecute
- Event callbacks for monitoring batch operations
- Error handling for failed batch operations
- Automatic or manual batch processing
- All stateful properties (items, counts, etc.) are exposed as Solid signals for reactivity

The batcher collects items and processes them in batches based on:
- Maximum batch size (number of items per batch)
- Time-based batching (process after X milliseconds)
- Custom batch processing logic via getShouldExecute

Error Handling:
- If an `onError` handler is provided, it will be called with the error and batcher 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 AsyncBatcher 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 `batcher.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:
- `errorCount`: Number of failed batch executions
- `executionCount`: Total number of batch execution attempts (successful + failed)
- `hasError`: Whether the last batch execution resulted in an error
- `isExecuting`: Whether a batch execution is currently in progress
- `items`: Array of items currently queued for batching
- `lastError`: The error from the most recent failed batch execution (if any)
- `lastResult`: The result from the most recent successful batch execution
- `settleCount`: Number of batch executions that have completed (successful or failed)
- `successCount`: Number of successful batch executions

## Unmount behavior

By default, the primitive cancels any pending batch 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 batcher = createAsyncBatcher(fn, {
  maxSize: 10,
  wait: 2000,
  onUnmount: (b) => b.flush()
});
```

Note: For async utils, `flush()` returns a Promise and runs fire-and-forget in the cleanup.
If your batch 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.

Example usage:
```tsx
// Default behavior - no reactive state subscriptions
const asyncBatcher = createAsyncBatcher(
  async (items) => {
    const results = await Promise.all(items.map(item => processItem(item)));
    return results;
  },
  {
    maxSize: 10,
    wait: 2000,
    onSuccess: (result) => {
      console.log('Batch processed successfully:', result);
    },
    onError: (error) => {
      console.error('Batch processing failed:', error);
    }
  }
);

// Opt-in to track items or isExecuting changes (optimized for UI updates)
const asyncBatcher = createAsyncBatcher(
  async (items) => {
    const results = await Promise.all(items.map(item => processItem(item)));
    return results;
  },
  { maxSize: 10, wait: 2000 },
  (state) => ({ items: state.items, isExecuting: state.isExecuting })
);

// Opt-in to track error state changes (optimized for error handling)
const asyncBatcher = createAsyncBatcher(
  async (items) => {
    const results = await Promise.all(items.map(item => processItem(item)));
    return results;
  },
  { maxSize: 10, wait: 2000 },
  (state) => ({ hasError: state.hasError, lastError: state.lastError })
);

// Add items to batch
asyncBatcher.addItem(newItem);

// Manually execute batch
const result = await asyncBatcher.execute();

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

## Type Parameters

### TValue

`TValue`

### TSelected

`TSelected` = \{
\}

## Parameters

### fn

(`items`) => `Promise`\<`any`\>

### options

[`SolidAsyncBatcherOptions`](../interfaces/SolidAsyncBatcherOptions.md)\<`TValue`, `TSelected`\> = `{}`

### selector

(`state`) => `TSelected`

## Returns

[`SolidAsyncBatcher`](../interfaces/SolidAsyncBatcher.md)\<`TValue`, `TSelected`\>