Resposexml返回null值

Question

I am new to ajax. I wanted to create a simple webpage where it contains a button if clicked returns image dynamically.But the responseXML returns null value. Here is part of javascript code:

function process()
{
    if(xmlhttp.readyState==4 || xmlhttp.readyState==0)
    {
        xmlhttp.open("GET","image.php",true);
        xmlhttp.onreadystatechange = handleserverresponse;
        xmlhttp.send();
    }else{
        setTimeout('process()',1000);
    }
}

function handleserverresponse()
{
    if(xmlhttp.readyState==4){
        if(xmlhttp.status==200){    
            xmlResponse = xmlhttp.responseXML;
            imag = xmlResponse.documentElement.firstChild.data;
            document.getElementById("divimg").innerHTML=imag;
        }
        else{
            alert("something went wrong");
        }
    }

here is php code:

<?php
header('Content-Type:text/xml');
echo '<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>';

echo "<res>";
echo "<img src="a.jpg"/>";
echo "</res>";

?>

Answer 1

The reason responseXML was null because there is a mistake in PHP file. I guess We cannot send HTML tags when content type is xml. Instead what we can do is echo source of image and modify JavaScript file to take that source and display using img tag.