/**
 * padZero
 *
 * @example
 * ```ts
 * padZero(1)
 * // => 01
 * padZero(5)
 * // => 05
 * padZero(10)
 * // => 10
 * padZero(1, 3)
 * // => 001
 * ```
 */
export declare function padZero(value: number | string, len?: number): string;