title: Didn't defined variable in javascript but code is still working why?
body: <p>in this i didn't defined now variable but when i run code in console it is working why?</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>var year, yearJohn, yearMark;
  now = 2018
  year = 2018;
  yearJohn = year - 28;
  yearMark = year - 33;
  console.log(yearJohn, yearMark);
  console.log(now + 2);</code></pre>
  </div>
  </div>
  </p>
  
  <p>i expect the output of code will be syntax error, but the actual outpur is 2020.</p>