react是如何获取组件对应的DOM元素？

import React, { Component, createRef, useRef } from "react";

export default function GetDom() {
  return (
    <div>
      <GetDomClass />
      <GetDomFunc />
    </div>
  );
}

class GetDomClass extends Component {
  constructor(props) {
    super(props);
    this.divRef = createRef(null);
  }
  componentDidMount() {
    if (this.divRef.current) {
      console.log(this.divRef.current);
    }
  }
  render() {
    return <div ref={this.divRef}>GetDom</div>;
  }
}

function GetDomFunc() {
  const inputRef = useRef("null");
  return (
    <div>
      <input ref={inputRef} />
      <button onClick={() => inputRef.current?.focus()}>focus</button>
    </div>
  );
}