onePureFuncComp.js

import React, { useState, Fragment } from "react";

const WelcomeMessage = React.memo(({ name }) => {
  console.log("render WelcomeMessage");
  return <label>Hello {name}</label>;
});

const Page = () => {
  const [user, setUser] = useState({});
  console.log("render Page");

  return (
    <Fragment>
      <WelcomeMessage name={user.name} />
      <button onClick={() => setUser({ name: "Jack", age: 42 })}>
        Set user
      </button>
    </Fragment>
  );
};