import type { DataWithResponseInit } from './interfaces.js';
/**
 * Returns a function that can only be called once.
 * Subsequent calls will return the result of the first call.
 * This is useful for lazy initialization.
 * @param fn - The function to be called once.
 * @returns A function that can only be called once.
 */
export declare function lazy<T>(fn: () => T): () => T;
/**
 * Returns true if the response is a redirect.
 * @param res - The response to check.
 * @returns True if the response is a redirect.
 */
export declare function isRedirect(res: Response): boolean;
/**
 * Returns true if the response is a JSON response.
 * This is determined by checking if the Content-Type header includes 'application/json'.
 * @param res - The response to check.
 * @returns True if the response is a JSON response.
 */
export declare function isJsonResponse(res: Response): boolean;
/**
 * Returns true if the response is a response.
 * @param response - The response to check.
 * @returns True if the response is a response.
 */
export declare function isResponse(response: unknown): response is Response;
/**
 * Checks if the data is a DataWithResponseInit object.
 * @param data - The data to check.
 * @returns True if the data is a DataWithResponseInit object.
 */
export declare function isDataWithResponseInit(data: unknown): data is DataWithResponseInit<unknown>;