react中使用context（上下文）

import React, { Component } from 'react';
import './App.css';
import PropTypes from 'prop-types';

const Topic = (props) => {
  return (
    <div>
      <Comment />
    </div>
  )
}

const Comment = (props, context) => {
  return (
    <div>{ context.color }</div>
  )
}

Comment.contextTypes = {
  color: PropTypes.string
}

class App extends Component {
  getChildContext() {
    return { color: "red" };
  }
  render() {
    return (
      <div className="App">
        <Topic />
      </div>
    );
  }
}

App.childContextTypes = {
  color: PropTypes.string
}

export default App;