The Multilink Pattern

When a callback needs to react to several Properties at once, don't link to each one and re-run the same logic from multiple call sites — use Multilink.multilink, which fires once with the current value of every dependency, and again whenever any of them changes. It's the side-effecting sibling of DerivedProperty: use DerivedProperty when the combination produces a new value to store, use Multilink when it produces an effect (a repaint, a sound, a log line) with no value to keep.

The core idea

import { Multilink, NumberProperty, BooleanProperty } from 'scenerystack/axon';

const massProperty = new NumberProperty( 5 );
const gravityProperty = new NumberProperty( 9.8 );
const isPausedProperty = new BooleanProperty( false );

// Fires immediately with the current values, then again on every subsequent change.
const multilink = Multilink.multilink(
  [ massProperty, gravityProperty, isPausedProperty ],
  ( mass, gravity, isPaused ) => {
    console.log( `weight = ${ mass * gravity } N, paused = ${ isPaused }` );
  }
);

// Later, if this reaction has a lifetime shorter than its dependencies:
Multilink.unmultilink( multilink );

new Multilink( dependencies, callback, lazy? ) is the equivalent instance form — reach for it only when you need a handle without going through the static helper (for example, to pass lazy: true and skip the initial call). Prefer Multilink.multilink for the common case, since constructing a Multilink you never reference is just an unused variable with no compensating benefit.

Multilink vs. DerivedProperty

	Multilink	DerivedProperty
Produces	Nothing — runs a callback	A new TReadOnlyProperty<T> value
Use when	The reaction is an effect (repaint a Node, play a sound)	The combination is state other code should read/observe
Disposal	Multilink.unmultilink( multilink )	derivedProperty.dispose()

import { DerivedProperty } from 'scenerystack/axon';

// Prefer this over a Multilink when the combined value is itself state:
const weightProperty = new DerivedProperty(
  [ massProperty, gravityProperty ],
  ( mass, gravity ) => mass * gravity
);

Dispose Multilinks that outlive their dependencies

Multilink.multilink returns the Multilink instance so you can call Multilink.unmultilink on it. If the object doing the linking (a Node, a view) is disposed before its dependency Properties are, failing to unmultilink leaks a listener on each dependency — see Dispose and Memory Management. If you don't need the handle because both sides share the same lifetime (e.g. a model linking its own Properties in its constructor), it's fine to ignore the return value.