ant-design/components/spin/usePercent.ts

import * as React from 'react';

const AUTO_INTERVAL = 200;
const STEP_BUCKETS: [limit: number, stepPtg: number][] = [
  [30, 0.05],
  [70, 0.03],
  [96, 0.01],
];

export default function usePercent(
  spinning: boolean,
  percent?: number | 'auto',
): number | undefined {
  const [mockPercent, setMockPercent] = React.useState(0);
  const mockIntervalRef = React.useRef<ReturnType<typeof setInterval>>(null);

  const isAuto = percent === 'auto';

  React.useEffect(() => {
    if (isAuto && spinning) {
      setMockPercent(0);

      mockIntervalRef.current = setInterval(() => {
        setMockPercent((prev) => {
          const restPTG = 100 - prev;

          for (let i = 0; i < STEP_BUCKETS.length; i += 1) {
            const [limit, stepPtg] = STEP_BUCKETS[i];

            if (prev <= limit) {
              return prev + restPTG * stepPtg;
            }
          }

          return prev;
        });
      }, AUTO_INTERVAL);
    }

    return () => {
      if (mockIntervalRef.current) {
        clearInterval(mockIntervalRef.current);
        mockIntervalRef.current = null;
      }
    };
  }, [isAuto, spinning]);

  return isAuto ? mockPercent : percent;
}