App.jsx

import React, { Component, PropTypes } from "react";
import io from "socket.io-client";

class App extends Component {
  constructor(props, context) {
    super(props, context);
    this.state = {
      message: null
    };
    this.socket = io("https://localhost:3001");
  }

  getChildContext() {
    return {
      socket: this.socket
    };
  }

  render() {
    return (
      <div>
        {this.props.children}
      </div>
    );
  }
}

App.propTypes = {
  children: PropTypes.object.isRequired
};

App.childContextTypes = {
  socket: PropTypes.object.isRequired
};

export default App;

HomePageComponent.jsx

import React, { Component, PropTypes } from 'react';

class HomePageComponent extends Component {
  constructor(props, context) {
    super(props, context);
    this.state = {
      message: null
    };
    this.socket = context.socket;
  }

  componentWillMount() {
    this.socket.on('welcome', (data) => {
      this.setState({ message: data.msg })
    });
  }

  render() {
    return (
      <div>
        {this.state.message}
      </div>
    );
  }
}

HomePageComponent.contextTypes = {
  socket: PropTypes.object.isRequired
};

export default HomePageComponent;