export interface IEventSource<T extends Function> {
    add(listener: T): () => void;
    remove(listener: T): void;
    trigger: T;
}
export declare class EventSource<T extends Function> implements IEventSource<T> {
    private _listeners;
    /** Registers a new listener for the event. */
    add(listener: T): () => void;
    /** Unregisters a listener from the event.
        If no listener is provided, removes all listeners */
    remove(listener?: T): void;
    /** Invokes all of the listeners for this event. */
    trigger: T;
}