title: Why this piece of code prints `undefined` at the end?
body: <p>While I am running the following piece of code in Chrome's developer tools javascript console,</p>
  
  <pre><code>var solution = 1;
  for(var i = 1; i &lt;= 12; ++i)
      solution *= i;
  console.log(solution.toString());
  </code></pre>
  
  <p>I get the following output:</p>
  
  <pre><code>479001600
  undefined
  </code></pre>
  
  <p>When I remove the last line, that is <code>console.log(solution.toString());</code>, I get just <code>479001600</code>. What happens?</p>