import type { ListenerTimer, Register, Unregister } from "../types";
/**
 * Calls `callback` at least every `duration` milliseconds. Returns a function that stops future calls of `callback`.
 * If the `duration` is `0`, it uses `requestAnimationFrame` if available.
 *
 * @param duration Minimum duration of each interval in milliseconds.
 * @param callback Called at the end of each interval.
 * @returns Function that cancels the interval.
 */
export declare function interval(duration: number, callback: ListenerTimer): Unregister;
/**
 * Returns a function that registers a `callback` to be called at least every `duration` milliseconds.
 * If the `duration` is `0`, if uses `requestAnimationFrame` if available.
 * The interval is set during this call.
 *
 * @param duration Minimum duration of each interval in milliseconds.
 * @returns Function that registers a callback to call at each elapsed interval, and returns a function that unregisters it. If the latter function unregisters the last callback, it clears the interval. When registering a callback on a cleared interval, throws an `Error` exception.
 */
export declare function interval(duration: number): Register<ListenerTimer, undefined>;