Storyden

export type Emitter<TEvents extends Record<string | symbol, unknown>> = { on<K extends keyof TEvents>( type: K, handler: (event: TEvents[K]) => void, ): void; off<K extends keyof TEvents>( type: K, handler: (event: TEvents[K]) => void, ): void; emit<K extends keyof TEvents>(type: K, event: TEvents[K]): void; }; export function createEmitter< TEvents extends Record<string | symbol, unknown>, >(): Emitter<TEvents> { const listeners = new Map<keyof TEvents, Set<(event: unknown) => void>>(); function on<K extends keyof TEvents>( type: K, handler: (event: TEvents[K]) => void, ) { let set = listeners.get(type); if (!set) { set = new Set(); listeners.set(type, set); } set.add(handler as (event: unknown) => void); } function off<K extends keyof TEvents>( type: K, handler: (event: TEvents[K]) => void, ) { const set = listeners.get(type); if (!set) return; set.delete(handler as (event: unknown) => void); if (set.size === 0) listeners.delete(type); } function emit<K extends keyof TEvents>(type: K, event: TEvents[K]) { const set = listeners.get(type); if (!set) return; // Copy to array to avoid issues if handlers mutate the set [...set].forEach((fn) => fn(event)); } return { on, off, emit }; }