title: Why can't I get properties count of navigator object in JavaScript?
body: <p>Run in your browser (ES5+)</p>
  
  <pre><code>var propCount = Object.keys(navigator).length;
  console.log(propCount); // 0
  </code></pre>
  
  <p>If you do it for a plain object like that</p>
  
  <pre><code>let obj = {
      foo: 'bar',
      breaking: 'bad'
  }
  
  let propCount = Object.keys(obj).length;
  
  console.log(propCount); // 2
  </code></pre>
  
  <p>Why does it happen?</p>
  
  <p>Sorry if it might relate to another problem like when <code>Object.keys(obj)</code> is only counting it for simple objects which do not contain <code>functions/arrays</code>, but this the 1st time I encountered with it.</p>
  
  <p>And would like to know the reason of it.</p>