vant/src-next/utils/dom/raf.ts

/**
 * requestAnimationFrame polyfill
 */

import { inBrowser } from '..';

let prev = Date.now();

/* istanbul ignore next */
function fallback(fn: FrameRequestCallback): number {
  const curr = Date.now();
  const ms = Math.max(0, 16 - (curr - prev));
  const id = setTimeout(fn, ms);
  prev = curr + ms;
  return id;
}

/* istanbul ignore next */
const root = (inBrowser ? window : global) as Window;

/* istanbul ignore next */
const iRaf = root.requestAnimationFrame || fallback;

/* istanbul ignore next */
const iCancel = root.cancelAnimationFrame || root.clearTimeout;

export function raf(fn: FrameRequestCallback): number {
  return iRaf.call(root, fn);
}

// double raf for animation
export function doubleRaf(fn: FrameRequestCallback): void {
  raf(() => {
    raf(fn);
  });
}

export function cancelRaf(id: number) {
  iCancel.call(root, id);
}