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Editorial Team
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Asked: 2026-06-01T14:48:45+00:00

I am learning to use xmlhttprequest/AJAX. In this sample code from w3schools, I do

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I am learning to use xmlhttprequest/AJAX. In this sample code from w3schools, I do not understand why this line:

document.getElementById("myDiv").innerHTML=xmlhttp.responseText;

precedes this:

 xmlhttp.open("GET","demo_get.asp",true);
 xmlhttp.send();

The way I’m thinking about it, you should send the GET request before you have any responseText to do anything with. Where is the error in my understanding?

<html>
<head>
<script type="text/javascript">
function loadXMLDoc()
{
var xmlhttp;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
    }
  }
xmlhttp.open("GET","demo_get.asp",true);
xmlhttp.send();
}
</script>
</head>
<body>

<h2>AJAX</h2>
<button type="button" onclick="loadXMLDoc()">Request data</button>
<div id="myDiv"></div>

</body>
</html>
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1 Answer

  1. Editorial Team

    The line in question is inside of xmlhttp.onreadystatechange, which is a function. Note how it is used:

    xmlhttp.onreadystatechange = function ()
{
    ...
}

    In this case, it is a callback function – it is called when the ajax request (aka xmlhttp.send()) completes.

    You might want to brush up on your javascript before you dive into ajax.

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