title: i can't understand parseInt method in this code
body: <p>code is like that :)</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>function test3(num) {
    if (num &lt;= 9) {
      return num;
    }
    let rest = 1;
    while (num) {
      rest = rest * (num % 10);
      num = parseInt(num / 10);
    }
    if (rest &lt;= 9) {
      return rest;
    }
    return test3(rest);
  }
  debugger;
  let output = test3(786);
  console.log(output); // --&gt; 0</code></pre>
  </div>
  </div>
  </p>
  <p>i understand other logic but, i dont understand 'parseInt'
  how to work parseInt logic ?
  apparently i m already read mdn, and any stackover flow answer, can't understand well..</p>