Find out weather a tab has rendered content or not

Add-ons Development
#1

I looked at https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/tabs/Tab

I use
browser.tabs.get(tabId)

  • but the returned value is status:undefined and index: NaN

however the id is correct, as
browser.tabs.remove(tabId)
closes the tab in question.

What I intend to find out is, weather the tab with tabId has rendered content. This is slightly different from determining the status or URL i think, because when a tab is redirected there is an URL but no rendered content)