/// <reference types="@rbxts/compiler-types" />
/**
 * Calls a function every `interval` seconds until the countdown reaches 0.
 * Returns a promise that resolves when the countdown is over. Canceling the
 * promise will stop the countdown.
 * @param callback The callback to call every second.
 * @param countdown The countdown in seconds.
 * @param interval The interval in seconds.
 * @returns A promise that resolves when the countdown reaches 0.
 */
export declare function setCountdown(callback: (secondsLeft: number) => void, countdown: number, interval?: number): Promise<number[]>;