title: console.log doesn’t print anything but returns undefined
body: <p>I have made a script to grab all the sentences I’m learning on duolingo into one single console.log output. 
  It worked perfectly until recently, when console.log started behave in a strange way :</p>
  
  <pre><code>console.log("Hello\tWorld")
  undefined
  </code></pre>
  
  <p>whatever I type in console.log doesn’t get printed at all</p>
  
  <pre><code>console.log(document)
  undefined
  </code></pre>
  
  <p>this only happens on this particular page : 
  <a href="https://www.duolingo.com/practice" rel="nofollow noreferrer">https://www.duolingo.com/practice</a>
  (you need to be logged in)</p>
  
  <p>Is it even a thing ? to block a function like console.log on your page, preventing it from printing any result at all?</p>
  
  <p>is there a way to print something in the console despite that ?</p>