Angular Batching Guide

Batching collects items and passes them to one function as an array. A batch can run when it reaches a configured size, after no new items arrive for a configured wait, or when custom logic says it is ready.

Batching reduces the number of operations by processing several items together. Unlike queuing, it does not call the wrapped function once for each item.

How batching works

plaintext

Batching (process every 3 items or after 2 quiet ticks)
Timeline: [1 second per tick]
Calls:        ⬇️  ⬇️  ⬇️     ⬇️  ⬇️             ⬇️  ⬇️  ⬇️
Batch:       [ABC]   []      [DE]      []        [FGH]  []
Executed:     ✅              ✅                  ✅
             [======================================================]
             ^ Items are grouped and processed together

             [Size reached]   [Wait elapsed]      [Size reached]

Each execution receives a copy of the items currently collected. The batcher clears those items before calling the wrapped function.

When to use batching

Choose batching when:

A bulk operation is more efficient than individual operations.
Network requests, database writes, or analytics events can be grouped.
A maximum batch size or quiet-period trigger matches the workload.
Individual item results are unnecessary.

Choose another utility when:

Every item should run individually and in order. Use queuing.
Only the latest value matters. Use debouncing.
Calls should be spaced over time. Use throttling.
Batch processing returns a Promise or needs retries and abort support. Use async batching.

Choose an API

injectBatchedCallback for an item-adder
injectBatcher for flush, cancel, collected items, and selected state

Use the callback API when adding items is all the component needs. Use the instance API for flush(), cancel(), collected items, selected state, and dynamic options.

Angular example

import { injectBatchedCallback, injectBatcher } from '@tanstack/angular-pacer'

export class AnalyticsComponent {
  readonly addEvent = injectBatchedCallback(sendEvents, {
    maxSize: 20,
    wait: 1000,
  })
  readonly batcher = injectBatcher(
    sendEvents,
    { maxSize: 20, wait: 1000 },
    (state) => ({
      size: state.size,
    }),
  )
}

The focused snippets later in this guide use injectBatcher and assume they run inside an Angular injection context.

Choosing batch triggers

Batch size

maxSize executes the batch as soon as the number of collected items reaches the limit.

const batcher = injectBatcher(processBatch, {
  maxSize: 100,
})

The default is Infinity, so a size trigger is disabled unless you provide one.

Wait time

wait executes a batch after no new items arrive for the configured duration. Every added item restarts the timer.

const batcher = injectBatcher(processBatch, {
  wait: 1000,
})

The default is Infinity, so a time trigger is disabled unless you provide one. A continuous stream of items can keep restarting the timer. Combine wait with maxSize when a batch must eventually run under continuous traffic.

Custom trigger

getShouldExecute runs after each item is added. Return true to execute the current batch immediately.

const batcher = injectBatcher<number>(processBatch, {
  getShouldExecute: (items) => items.includes(0),
})

batcher.addItem(4)
batcher.addItem(0) // Executes [4, 0].

If several triggers are configured, the first one reached executes the batch.

Controlling collected items

Flush

flush() clears the pending timer and executes all currently collected items. It does nothing when the batch is empty.

batcher.addItem('event-1')
batcher.addItem('event-2')
batcher.flush()

Cancel

cancel() clears the pending timer but keeps the collected items. A later item can schedule a new timer, or you can call flush().

batcher.cancel()
console.log(batcher.peekAllItems()) // Items are still present.

Clear

clear() removes all collected items. It does not clear the timer itself, although that timer has no items to execute unless more items are added.

batcher.clear()

Reset

reset() restores batch state and counters to their defaults. It does not cancel an already scheduled timer. Call cancel() before reset() when pending work must be discarded.

batcher.cancel()
batcher.reset()

Configuring and observing batches

Use setOptions() to update future trigger behavior:

batcher.setOptions({
  maxSize: 20,
  wait: 500,
})

Changing wait does not reschedule an existing timer. The next addItem() call replaces that timer using the current value.

The wait option may be a function that receives the batcher instance:

const batcher = injectBatcher(processBatch, {
  wait: (batcher) => (batcher.store.state.size > 10 ? 100 : 500),
})

Use onItemsChange to observe collection changes and onExecute to observe completed batch calls:

const batcher = injectBatcher(processBatch, {
  maxSize: 10,
  onItemsChange: (batcher) => {
    console.log('Collected:', batcher.store.state.size)
  },
  onExecute: (items, batcher) => {
    console.log('Processed:', items)
    console.log('Batches:', batcher.store.state.executionCount)
  },
})

Do not use started to pause a batcher. It is currently a no-op, so every addItem() call evaluates the configured triggers.

Angular lifecycle

The adapter cancels the pending wait timer while retaining collected items when its owner is destroyed. Providing onUnmount replaces that default cleanup, so a custom callback must perform every required lifecycle action. When custom cleanup flushes work, remember that user callbacks can run while the component is being destroyed.

Reactive state

The adapter subscribes only to the state returned by the selector argument. Without a selector, the adapter state is empty. Create the utility in an Angular injection context, usually as a component or service field initializer and select only fields used by the view:

const batcher = injectBatcher(
  processBatch,
  { maxSize: 20, wait: 1000 },
  (state) => ({
    size: state.size,
    isPending: state.isPending,
  }),
)

console.log(batcher.state().size, batcher.state().isPending)

Option functions and lifecycle callbacks receive the underlying public utility instance. The .store.state reads inside those callbacks in the examples above are supported. Rendering code should read the selected adapter state shown here.

To restore selected state that your app has persisted, pass a partial snapshot through initialState. It is merged with the defaults. Restore only durable fields. Pending timers are not restored.

Commonly useful state includes: