import { TimeMachineDate } from "../types";
/**
 * Check if value is a number, or if a string can be parsed into a number.
 *
 * @param value Value to check.
 * @returns `true` if it is a valid number.
 */
export declare function isNumber(value: any): boolean;
/**
 * Check if a value is an object.
 *
 * @param value Variable to check if it is an object.
 * @returns `true` if value is an object.
 */
export declare function isObject(value: any): boolean;
/**
 * Convert a [[TimeMachineDate]] into a Unix timestamp value that OpenWeatherMap accepts.
 *
 * @param time The TimeMachineDate value to be converted into a Unix timestamp.
 * @returns `undefined` if the property is not set, and a Unix timestamp if defined.
 * @throws Error if [[time]] is not a number or a [[Date]] object.
 */
export declare function parseTimeMachineDate(time?: TimeMachineDate): number | undefined;