Chrome Extension - 2 way communication

background.js

'use strict';

function sendMessage() {
  chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
    chrome.tabs.sendMessage(tabs[0].id, "Background page started.");
  });
}

function update() {
  console.log('update')
  sendMessage();
};

chrome.browserAction.onClicked.addListener(update);

chrome.runtime.onMessage.addListener(function(msg) {
  console.log(msg);
});

contentscript.js

console.log('Hello from Content Script'); 

chrome.runtime.sendMessage({ horde: true });

chrome.runtime.onMessage.addListener(function(msg, _, sendResponse) {
  console.log("Got message from background page: " + msg);
});

manifest.json

{
  "name": "Earth Particle",
  "version": "0.0.1",
  "manifest_version": 2,
  "description": "This extension adds chaos to your project",
  "homepage_url": "http://telus.com",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "default_locale": "en",
  "background": {
    "scripts": [
      "src/background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_title": "Release Chaos"
  },
  "permissions": [
    "contentSettings",
    "tabs",
    "https://*/*",
  ],
  "content_scripts": [
    {
      "matches": [
        "https://*/*"
      ],
      "js": [
        "src/contentscript.js"
      ]
    }
  ]
}