Untracked

Runs a callback function fn that can read signal values without establishing a reactive subscription.

Normally, reading a signal's value (via .value or ()) inside an effect or a computed callback automatically subscribes the surrounding context to that signal. If the signal changes, the context is re-executed.

In some scenarios, you want to read a signal's current value inside a reactive context but avoid creating a subscription. This is where untracked is useful. It temporarily suspends active tracking, executes fn, and then restores tracking.

Parameters:

• fn: The callback function to execute. Any signal read inside this callback will not register a dependency.

Returns:

• The value returned by the callback function fn.

Example Usage#

import 'package:preact_signals/preact_signals.dart';

void main() {
  final counter = signal(0);
  final loggingThreshold = signal(5);

  effect(() {
    final currentCount = counter.value; // Establishing a subscription to `counter`

    // We want to read `loggingThreshold` but we do NOT want this effect to
    // trigger whenever `loggingThreshold` changes.
    final threshold = untracked(() => loggingThreshold.value);

    if (currentCount > threshold) {
      print("Counter ($currentCount) has exceeded the threshold ($threshold)!");
    }
  });

  counter.value = 6; // Prints: "Counter (6) has exceeded the threshold (5)!"

  // Updating the threshold will NOT trigger the effect, because it was read inside `untracked`
  loggingThreshold.value = 10;
}