title: How do i use removeEventListener to remove event?
body: <p>HTML </p>
  
  <pre><code>&lt;button id="btn" value="250"&gt;Click Me&lt;/button&gt;
  </code></pre>
  
  <p>JS </p>
  
  <pre><code>document.getElementById('btn').addEventListener('click',say,false);
  
  function say() {
   alert("this is add function !!!");
   this.removeEventListener('click',function () {
    alert("this is remove function");
    },false);
  } 
  </code></pre>
  
  <p>I want that functionality on my button that if user click first time than alert box show "this is add function" but second time click than alert bix show "this is remove function" &amp; third time again show "this is a add function" , this will continue.</p>