javascript - Why is chrome.runtime undefined in the content script?

Question

I have a very simple chrome extension, where I'm trying to pass a message from the background script to the content script. But chrome.runtime is undefined.

Here's literally all the code, as you can see there's almost nothing to it. In the content script, runtime is undefined.

Background Script:

chrome.browserAction.onClicked.addListener(function(tab) {
  chrome.runtime.sendMessage({action: 'someAction'}, 
    function(response) {
      console.log('Response: ', response);
    });
});

Content Script:

chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
  sendResponse({
    user: 'user'
  });
});

manifest.json

{
  "manifest_version": 2,
  "name": "My Extension",
  "version": "1.0",

  "description": "Some stupid extension",

  "browser_action": {
    "default_icon": "icons/MyExtensionIcon.png"
  },
  "icons": {
    "48": "icons/MyExtensionIcon.png"
  },
  "permissions": [
    "tabs",
    "storage",
    "https://*/",
    "http://*/"
  ],
  "content_scripts": [
    {
      "matches": ["*://*.twitter.com/*", "https://twitter.com/*"],
      "js": ["js/content.js"]
    }
  ],
  "background": {
    "scripts": ["js/background.js"],
    "persistent": true
  },
  "web_accessible_resources": [
    "js/*",
    "css/*"
  ]
}

Other Info:

• Chrome Version 58.0.3029.110 (64-bit)
• Installing my extension as an "Unpacked extension" with developer mode

Answer 1

Ok I figured it out. It's absolutely stupid, but it appears this is simply a Heisenbug. By adding a breakpoint, or debugger statement, it causes that value to be undefined. Maybe a chrome bug?

I swear, every day Chrome feels more, and more like Internet Explorer.