/**
 * Expose ability to emit and subscribe to a single type of event.
 * @template TArg type of the event payload.
 */
export declare class EventEmitter<TArg = void> {
    private _handlers;
    /**
     * Subscribes to the event.
     * @param handler a function to call when the event has been fired.
     * @returns a token used to cancel the event subscription.
     * @remarks
     * * Subscribing the same handler multiple times is allowed; they will be invoked multiple times.
     * * If `handler` returns a {@link PromiseLike} value, depending on how the {@link EventEmitter.invokeAsync} is called,
     *    your event handler might be called concurrently (the 2nd invocation starts before the 1st invocation ends).
     * @todo Set up convention on what should happen if a handler is added/removed while
     * the event is being fired.
     */
    subscribe(handler: EventHandler<TArg>): Disposable;
    /**
     * Fires the event.
     * @param arg event payload.
     * @remarks
     * * This function will asynchronously wait for all its event handlers to return (or throw)
     * before returning, but _will not_ await any asynchronous portions.
     * * Were any of the event handler to throw any error, this function
     * _would not_ throw. Instead, errors are thrown to the current {@link SynchronizationContext}.
     */
    invoke(arg: TArg): void;
    /**
     * Fires the event asynchronously.
     * @param arg event payload.
     * @remarks
     * * This function will wait for all its event handlers to return (or throw)
     * before returning, and will await any asynchronous portions.
     * * Were any of the event handler to throw any error, this function
     * _would not_ throw. Instead, errors are thrown to the current {@link SynchronizationContext}.
     */
    invokeAsync(arg: TArg): Promise<void>;
}
export type SyncEventHandler<TArg> = (this: void, arg: TArg) => void;
export type AsyncEventHandler<TArg> = (this: void, arg: TArg) => void | PromiseLike<void>;
export type EventHandler<TArg> = SyncEventHandler<TArg> | AsyncEventHandler<TArg>;
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