/**
 * A record of events emitted by an [[EventEmitter]],
 * mapping from event name to event type.
 *
 * Events records are only intended for type bookkeeping,
 * not for use by literal objects or classes.
 */
export interface EventsRecord {
    [eventName: string]: any;
}
/**
 * Classes extending EventEmitter can emit events, and listeners can listen
 * on events using [[on]].
 *
 * @typeParam Events An interface mapping event names to event types.
 *
 * @remarks
 * Inspired by {@link https://github.com/ai/nanoevents | nanoevents}, but
 * refactored as a class to better fit into our class hierarchy.
 */
export declare class EventEmitter<Events extends EventsRecord> {
    /**
     * Maps event names to registered handlers.
     *
     * Properly, `any` should instead be `this`.  However,
     * that causes errors when trying to treat a Collab
     * subclass as an instance of Collab, for reasons
     * that are not clear to me.
     */
    private readonly handlers;
    /**
     * Registers an event handler that is triggered when the event happens.
     *
     * @param eventName Name of the event to listen on.
     * @param handler Callback that handles the event.
     * @param options.once If true, the event handler is triggered at most
     * once (the next time the event happens), then unsubscribed.
     * @return An "off" function that removes the event handler when called.
     */
    on<K extends keyof Events>(eventName: K, handler: (event: Events[K], caller: this) => void, options?: {
        once?: boolean;
    }): () => void;
    /**
     * Emits an event, which triggers all the registered event handlers.
     *
     * Event handlers are called in the order they are added. Errors in
     * event handlers are captured and logged (with `console.error`),
     * not propagated to the caller.
     *
     * @param eventName Name of the event to emit.
     * @param event Event object to pass to the event handlers.
     */
    protected emit<K extends keyof Events>(eventName: K, event: Events[K]): void;
}