/**
 * Encodes a string to Base64.
 * @param {string} [inputString=''] - The string to encode.
 * @returns {string} The Base64 encoded string.
 * @example
 * const encoded = toBase64('Hello World'); // 'SGVsbG8gV29ybGQ='
 */
export declare function toBase64(inputString?: string): string;