Accessing console and devtools of extension's background.js

Question

You're looking at the wrong place. These console messages do not appear in the web page, but in the invisible background page (ManifestV2) or service worker (ManifestV3).

To view the correct console open devtools for the background script's context:

1. Visit chrome://extensions/ or right-click the extension icon and select "Manage extensions".
2. Enable developer mode
3. Click on the link named background page (ManifestV2) or service worker (ManifestV3).

Screenshot for ManifestV2 extensions:

Screenshot for ManifestV3 extensions:

I had the same problem, in my case the logging was set to "Hide all" in the console tab in Chrome Developer tools. I had not even realised this was an option, and I can't remember turning it off

For followers who wish to see the debug console for a "content script" of their chrome extension, it is available by doing a normal "show developer console" then use the dropdown arrow to selects its "javascript environment" then you'll have access to its methods, etc.

additionally

if you want to see content_script js file ( when "background" property is not set ) in manifest.json

"content_scripts": [{
    "matches": ["<all_urls>"],
    "js": ["popup.js"],
  }]

"browser_action": {
    "default_icon": "icon_32.png",
    "default_popup": "popup.html"
  }

then right click on extension icon and click on Inspect popup and developer window opens with popup.html opened , there you see console tab.