/**
 * Event Bus — lightweight publish/subscribe event system.
 *
 * Enables decoupled communication between components across the page
 * without direct DOM access or custom element references.
 *
 * @example
 * // Publish
 * eventBus.emit('user:login', { userId: '123' });
 *
 * // Subscribe
 * const off = eventBus.on('user:login', ({ userId }) => { ... });
 * off(); // unsubscribe
 *
 * // Wait for a single event
 * const data = await eventBus.once('data:ready');
 */
type EventHandler<T = unknown> = (data: T) => void;
declare class EventBus {
    private _subs;
    private _history;
    /** Subscribe to an event. Returns an unsubscribe function. */
    on<T = unknown>(event: string, handler: EventHandler<T>): () => void;
    /** Subscribe to an event once. Auto-unsubscribes after first emission. */
    once<T = unknown>(event: string, handler?: EventHandler<T>): Promise<T>;
    /** Emit an event with optional data. */
    emit<T = unknown>(event: string, data?: T): void;
    /** Unsubscribe all handlers for an event (or all events if no event given). */
    off(event?: string): void;
    /** Get number of subscribers for an event. */
    listenerCount(event: string): number;
    /** Get all active event names. */
    eventNames(): string[];
    /**
     * Subscribe and immediately receive the last emitted value if available (replay).
     * Useful for late subscribers who may miss earlier emissions.
     */
    replay<T = unknown>(event: string, handler: EventHandler<T>): () => void;
    /** Clear the replay history for an event. */
    clearHistory(event?: string): void;
}
/** Global singleton event bus */
export declare const eventBus: EventBus;
/**
 * Create a namespaced event bus — useful for scoping events per feature/module.
 * @example
 * const cartBus = createEventBus('cart');
 * cartBus.emit('item:added', item); // internally emits 'cart:item:added'
 */
export declare function createEventBus(namespace: string): {
    on<T>(event: string, handler: EventHandler<T>): () => void;
    once<T>(event: string): Promise<T>;
    emit<T>(event: string, data?: T): void;
    off(event?: string): void;
};
export type { EventHandler };
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