问React - prop-types被标记为required

EN

// index.js
import React, { Component } from "react";
import { render } from "react-dom";
import Rate from "./components/Rate";
import Card from "./components/Card";

class App extends Component {
  state = {
    loading: true
  };

  componentDidMount() {
    setTimeout(() => this.setState({ loading: false, rate: 5 }), 5000);
  }

  render() {
    return (
      <Card loading={this.state.loading}>
        <Rate rate={this.state.rate} />
      </Card>
    );
  }
}

render(<App />, document.getElementById("root"));

// rate.js
import React from "react";
import PropTypes from "prop-types";

const Rate = ({ rate }) => (
  <div>
    <span>{rate}/10</span>
  </div>
);

Rate.propTypes = {
  rate: PropTypes.number.isRequired
};

export default Rate;