export type Listener<T> = (payload: T) => void;
/**
 * Minimal typed event emitter backing the puppeteer-style Page event API.
 *
 * The optional `onCountChange` hook fires whenever an event's listener count
 * changes (adds, removes, `once` auto-removal, `removeAllListeners`). Page uses
 * it to lazily open a subscription on the 0→1 transition and close it on 1→0.
 *
 * Listeners are stored in a `Set`, so registering the *same* function twice for
 * an event is deduped to a single registration (one `emit` call, one `off` to
 * remove) — unlike Node's `EventEmitter`, which keeps duplicates. This is
 * intentional: it keeps the 0→1/1→0 count transitions that drive lazy
 * subscriptions unambiguous. Wrap in distinct closures if you need duplicates.
 */
export declare class EventEmitter<Events> {
    #private;
    private readonly onCountChange?;
    constructor(onCountChange?: ((event: keyof Events, count: number) => void) | undefined);
    on<K extends keyof Events>(event: K, listener: Listener<Events[K]>): this;
    off<K extends keyof Events>(event: K, listener: Listener<Events[K]>): this;
    once<K extends keyof Events>(event: K, listener: Listener<Events[K]>): this;
    /** Invoke every listener for `event`. Returns whether any listener ran. */
    emit<K extends keyof Events>(event: K, payload: Events[K]): boolean;
    listenerCount<K extends keyof Events>(event: K): number;
    removeAllListeners<K extends keyof Events>(event?: K): this;
}
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