title: ClearInterval not clearing SetInterval
body: <p>When we call clearInterval with the value returned by SetInterval  does it make that value null or undefined. </p>
  
  <p>I am calling clearInterval to clear setInterval but apparently value of setInterval remains same and does not change even after calling clearInterval . Is t suppposed to be null or undefined ? Here is my code snippet </p>
  
  <pre><code>var setIntervalId; // declared in global scope
  //lined of code
  
  function autorefresh() {
    if (statesCount &gt; 0) {
      setIntervalId = setInterval(function() {
          //lines of code
          // calling some handler
      }, 30000);
    }
  
    if (statesCount === 0) {
      clearInterval(setIntervalId);
    }
  }
  </code></pre>
  
  <p>As you can see I am calling my setInterval function every 30 seconds , when called for the first time assigns some value to setIntervalId , but even after calling clearInterval the value persists. Should it become null or undefined after calling clearInterval?If it should be null or undefined what should I do here.I have defined setIntervalId in global scope.</p>