Zylem Behaviors

The simulation layer of the Zylem framework: tree-shakable behavior descriptors, FSMs, coordinators, and the Simulation API that owns the @zylem/runtime WASM module (ECS + Rapier physics).

@zylem/behaviors sits between the game framework and the runtime:

@zylem/game-lib  →  @zylem/behaviors  →  @zylem/runtime (WASM)

• createSimulation() / Simulation — loads and owns the WASM stage, exposes spawn/despawn with opaque EntityHandles, a fixed-timestep update(delta) loop, snapshot/pose accessors, raycasts, debug rendering, and translated SimulationEvents (collision start/stop with handles instead of raw slots).
• Behavior descriptors (Platformer3DBehavior, TopDownMovementBehavior, …) — attach WASM-side controllers to entities and forward per-frame input through slot-indexed buffers; FSM state is read back from snapshots.
• MockBehaviorRuntime — in-memory BehaviorRuntime implementation for unit-testing behaviors without loading WASM.

Physics simulation is WASM-only; there is no TypeScript physics fallback. Disposal chains downward: Simulation.dispose() destroys the WASM stage.

Use per-behavior entrypoints when you want bundlers to pull only the behavior family you import:

import { ScreenWrapBehavior } from '@zylem/behaviors/screen-wrap';
import { CooldownBehavior } from '@zylem/behaviors/cooldown';

The package is ESM-only and declares sideEffects: false.

Requirements

• Node >= 22.12.0
• pnpm >= 10.32.1

Commands

pnpm install
pnpm build
pnpm typecheck
pnpm test