title: How to detect the variable when used?
body: <p>how to call a function every call of a variable? is the code below is possible?
  i'm planning to call a function every time "num" is used..</p>
  
  <pre><code>if (num == 100 &amp;&amp; num== 200 &amp;&amp; num==300) {
    console.log('it works!');
  }
  </code></pre>