title: Batch
description: Batch multiple signal writes into one update
---

The `batch` function allows you to combine multiple signal writes into one single update that is triggered at the end when the callback completes.

```dart
import 'package:signals/signals.dart';

final name = signal("Jane");
final surname = signal("Doe");
final fullName = computed(() => name.value + " " + surname.value);

// Logs: "Jane Doe"
effect(() => print(fullName.value));

// Combines both signal writes into one update. Once the callback
// returns the `effect` will trigger and we'll log "Foo Bar"
batch(() {
	name.value = "Foo";
	surname.value = "Bar";
});
```

When you access a signal that you wrote to earlier inside the callback, or access a computed signal that was invalidated by another signal, we'll only update the necessary dependencies to get the current value for the signal you read from. All other invalidated signals will update at the end of the callback function.

```dart
import 'package:signals/signals.dart';

final counter = signal(0);
final _double = computed(() => counter.value * 2);
final _triple = computed(() => counter.value * 3);

effect(() => print(_double.value, _triple.value));

batch(() {
	counter.value = 1;
	// Logs: 2, despite being inside batch, but `triple`
	// will only update once the callback is complete
	print(_double.value);
});
// Now we reached the end of the batch and call the effect
```

Batches can be nested and updates will be flushed when the outermost batch call completes.

```dart
import 'package:signals/signals.dart';

final counter = signal(0);
effect(() => print(counter.value));

batch(() {
	batch(() {
		// Signal is invalidated, but update is not flushed because
		// we're still inside another batch
		counter.value = 1;
	});

	// Still not updated...
});
// Now the callback completed and we'll trigger the effect.
```
