App.js

/*global chrome*/
import React from 'react';
//import logo from './logo.svg';
import './App.css';
import Dashboard from "./components/Dashboard";


export default class App extends React.Component {
  componentWillMount() {
    chrome.runtime.onMessage.addListener(
      function(request, sender, sendResponse) {
        console.log(sender.tab ?
          "from a content script:" + sender.tab.url :
          "from the extension");
        if (request.greeting == "hello")
          sendResponse({farewell: "goodbye"});
      });
  }

  render() {
    return (
      <div className="App">
        <Dashboard/>
      </div>
    );
  }
}

Button.jsx

// This code gets called when I click a button, it's inside Dashboard -> Button

foo() {
chrome.runtime.sendMessage(getExtension(), {greeting: "hello"}, function(response) {
      console.log(response);
    });
}