How can I allow JS to work on each ajax requested page?

<script>

document.addEventListener('DOMContentLoaded', function(){

var execute_sendAjax1 = document.getElementById('executeAjax1');
  execute_sendAjax1.addEventListener('click', sendAjax1);

function sendAjax1(){
var xhr1= new XMLHttpRequest();

xhr1.onreadystatechange = function(){
	if(xhr1.readyState === 4){
		document.getElementById('ajax1').innerHTML= xhr1.responseText;
	
    /*<Allow JS on the requested page>*/	
   
    /*</Allow JS on the requested page>*/
		
	}
}
	xhr1.open('POST','page_2.php');
	xhr1.send();
}

});

</script>

<button id='executeAjax1'>Execute 1</button>

<h1>Page 1</h1>

<div id='ajax1'></div>

<script>

var execute_sendAjax2 = document.getElementById('executeAjax2');
  execute_sendAjax2.addEventListener('click', sendAjax2);
  
function sendAjax2(){
var xhr2= new XMLHttpRequest();

xhr2.onreadystatechange = function(){
	if(xhr2.readyState === 4){
		document.getElementById('ajax2').innerHTML= xhr2.responseText;
	
	/*<Allow JS on the requested page>*/	
      
    /*</Allow JS on the requested page>*/
	
	}
}
	xhr2.open('POST','page_3.php');
	xhr2.send();
}

</script>

<button id='executeAjax2'>Execute 2</button>

<h1>Page 2</h1>

<div id='ajax2'></div>

<script>

var execute_sendAjax3 = document.getElementById('executeAjax3');
  execute_sendAjax3.addEventListener('click', sendAjax3);
  
function sendAjax3(){
var xhr3= new XMLHttpRequest();

xhr3.onreadystatechange = function(){
	if(xhr3.readyState === 4){
		document.getElementById('ajax3').innerHTML= xhr3.responseText;
		
	/*<Allow JS on the requested page>*/	
     
    /*</Allow JS on the requested page>*/
		
	}
}
	xhr3.open('POST','page_4.php');
	xhr3.send();
}

</script>

<button id='executeAjax3'>Execute 3</button>

<h1>Page 3</h1>

<div id='ajax3'></div>

<h1>Page 4</h1>