/**
 * Requests for an animation frame, then invokes a callback, a custom
 * implementation of the native `requestAnimationFrame` function. If a native
 * `requestAnimationFrame` is unavailable, this function will simulate its
 * behavior using timeouts.
 *
 * @param callback Handler invoked upon the next animation frame.
 *
 * @returns The request ID as a result of `requestAnimationFrame` or
 *          `setTimeout` (when native `requestAnimationFrame` is unavailable).
 */
export declare function requestAnimationFrame(callback: (...t: any) => void): number;