React 进入页面以后自动 focus 到某个输入框（输入框在子组件中）

import React, { useState, useEffect } from 'react';

const FancyInput = React.forwardRef((props, ref) => (
  <input ref={ref} placeholder={props.placeholder} >
  </input>
));

function LoadingButton() {
  const ref = React.createRef();

  useEffect(() => {
    console.log(ref)
    ref.current.focus()
  }, [])
  return (
    <div className="m-test-wrap">
      <FancyInput ref={ref} placeholder="enter"></FancyInput>
    </div>
  );
}

export default LoadingButton;