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Asked: 2026-05-30T17:47:19+00:00

Why xhr.responseXML.getElementsByClassName(‘clazz’) doesn’t work? Here is the js: var xhr = new XMLHttpRequest(); xhr.onreadystatechange

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Why xhr.responseXML.getElementsByClassName(‘clazz’) doesn’t work?

Here is the js:

    var xhr = new XMLHttpRequest();

    xhr.onreadystatechange = function() {
         if (xhr.readyState == 4) {
            var happiness = xhr.responseXML.getElementsByClassName('clazz');

            //Uncaught TypeError: Cannot read property 'innerHTML' of undefined
            console.log("happiness ? " + happiness[0].innerHTML);
         }
    };

    //xhr.overrideMimeType("application/xml");
    xhr.open("GET", "xhr.php", true);
    xhr.send(null);

xhr.php contains the following:

<?php

header('Content-type: application/xml; charset=UTF-8');

echo "<?xml version=\"1.0\" encoding=\"UTF-8\"?> \n";

?>



<!DOCTYPE html>

<html>

<head>

<title>I'm the XHR response</title>

</head>

<body>



<div class="clazz">xhr happiness</div>



<div id="x" class="y"></div>



</body>

</html>

can you please explain the following output in the Chrome console?

xhr.responseXML.getElementById('x')
<div id="x" class="y"></div>

xhr.responseXML.getElementsByClassName('y')
[]
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1 Answer

  1. Editorial Team

    xhr.responseXML is XML nodes and not HTML elements which means that class attribute has not a special meaning.

    However, when I added xmlns declaration to the html tag, the getElementsByClassName on responseXML just worked (tested on Chrome).

    <html xmlns="http://www.w3.org/1999/xhtml">
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