/**
 * EventEmitter - 事件发射器
 * 用于实现上传/下载任务的事件机制
 */
declare const getList: unique symbol;
type Callback = (params?: any) => void;
interface Listener extends Callback {
    once?: boolean;
}
type Listeners = Record<string, Array<Listener>>;
declare class EventEmitter {
    listeners: Listeners;
    constructor();
    [getList](action: string): Array<Listener>;
    on(action: string, callback: Listener): EventEmitter;
    once(action: string, callback: Listener): EventEmitter;
    off(action: string, callback: Listener | '*'): EventEmitter;
    emit(action: string, data?: string | object): EventEmitter;
}
export default EventEmitter;