vant/packages/utils/raf.ts

/**
 * requestAnimationFrame polyfill
 */

import { isServer } from './index';

let prev = Date.now();

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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 = <Window>(isServer ? global : window);

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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);
}

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