Ferrsign

Typed event emitter optimized for hot paths.

What

Signal/event library with separate classes for 0-3 arguments: Ferrsign0, Ferrsign1<A>, Ferrsign2<A, B>, Ferrsign3<A, B, C>.

Why separate classes

Performance on old devices (iPad Pro 1st gen, iOS 13, etc.) in frame loops.

A unified emit(...args) API would require:

• Array allocation on every call
• Spread operator when invoking callbacks

At 60fps with multiple signals per frame, this creates GC pressure and microstutters. Separate classes with explicit emit(a, b) calls avoid both.

Usage

import { Ferrsign0, Ferrsign1, Ferrsign2 } from "ferrsign";

const onTick = new Ferrsign1<number>();
const onClick = new Ferrsign2<number, number>();
const onComplete = new Ferrsign0();

onTick.on((dt) => { /* dt: number */ });
onClick.on((x, y) => { /* x: number, y: number */ });
onComplete.once(() => { /* ... */ });

// In loop
onTick.emit(deltaTime);
onClick.emit(pointerX, pointerY);
onComplete.emit();

API

All classes share the same interface:

• on(callback) — subscribe
• once(callback) — subscribe, auto-unsubscribe after first emit
• off(callback) — unsubscribe
• emit(...) — notify subscribers (argument count matches class)

Read-only views

For exposing signals without emit access:

import { Ferrsign1, FerrsignView1 } from "ferrsign";

class Player {
  private readonly _onDamage = new Ferrsign1<number>();
  
  get onDamage(): FerrsignView1<number> { 
    return this._onDamage; 
  }
}

const player = new Player();
player.onDamage.on((amount) => { /* ... */ }); // ✓
player.onDamage.emit(10);  // ✗ Error — no emit on view

Available views: FerrsignView0, FerrsignView1<A>, FerrsignView2<A, B>, FerrsignView3<A, B, C>.

Limitations

• Max 3 arguments. If you need more, use an object:

  const onResize = new Ferrsign1<{ width: number; height: number }>();

• First 10 subscribers stored in direct slots, rest in array. Optimized for typical case of 1-5 listeners per signal.
• Dev-mode checks (duplicate subscription, unsubscribing non-existent callback) stripped in production build.

Safe during emit

Subscribing/unsubscribing during emit is handled correctly:

• New subscriptions are deferred until emit completes
• Removals mark slots for cleanup, no skipped/double calls