title: "Unexpected token ." when using optional chaning "?." syntax when running mocha
body: <p>I'm playing around with TS and encountered an error when trying to run a test for my code.
  I have a the following piece of code:</p>
  <pre><code>return this._map.get(y)?.get(x)
  </code></pre>
  <p>When I run the code for browser, everything works fine. When I run a test using <code>mocha</code>, however, it throws an error :</p>
  <pre><code>        return this._map.get(y)?.get(x);        
                                  ^
  
  SyntaxError: Unexpected token .
  </code></pre>
  <p>From what I managed to read, I'm supposed to configure <code>tsc</code> differently for NodeJS environment for things to work, but I was under the impression it was more about module resolution than syntax. Could it be that I need to upgrade to any specific NodeJS version? I've tried Node 10 through 13 but none worked.
  What am I missing?</p>