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Editorial Team
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Asked: 2026-06-14T09:38:38+00:00

I am trying to build a page that will display the next item in

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I am trying to build a page that will display the next item in a PHP array when the user clicks on a button. I’m a complete newbie on Ajax, and I am using the “Head First Ajax” book as a guide. My code (below) doesn’t work and I don’t understand why. Quite frankly, I am not even sure how to debug Ajax…

The code is in a file called Index.php. I am using WampServer.

The page loads properly. Here is the code:

<html><head><script type="text/javascript">
  var id=null;
  function getRequest(){
    try {
      request = new XMLHttpRequest();
    }catch (MS){
      try {
        request = new ActiveXObject("Msxml2.XMLHTTP");
      }catch (MoreMS){
        try {
          request = new ActiveXObject("Microsoft.XMLHTTP");
        }catch (failure){
          request = null;
        }
      }
    }
    return request;
  }

  function showNext(itemId){
    request=getRequest();
    if(request==null){
      alert("Request object is null");
      return;
    }
    var url="index.php?itemId="+escape(itemId);
    request.open("GET",url,true);
    request.onreadystatechange=function(){
      if(request.readyState==4){
        alert("Request.readyState is 4");
        if(request.status==200){
          alert("Request.status is 200");
          document.getElementById('article').value=request.responseText;
        }else{
          alert("Request.status not 200");
          return;
        }
      }else{
        alert("Request.readystate not 4");
        return;
      }
    }
    request.send(null);
  }

  function getItemId(){
    if(id==null){
      id=0;
    }else{
      id=id+1;
    }
    return id;
  }

  function doIt(){
    itemId=getItemId();
    showNext(itemId);
  }
</script></head>
<body><p>
  <textarea id='article'>
  </textarea>
</p>  
<p>
  <button type="button" id='showNext1' onclick="doIt()" >Show next</button>
</p></body></html>

<?php
  $array=array(10,21,32,43,54,65,76);
  if(!isset($_GET['itemId'])){
  }else{
    echo $array[$_GET['itemId']];
  }
  var_dump("GET :",$_GET);
?>

When I click the button, here is what happens:

I get twice the Request.readystate not 4 alert, then once Request.readyState is 4, then once Request.status is 200, then the textarea gets populated, and then again once Request.readystate not 4. After all that the textarea contains my entire code followed by this:

10<pre class='xdebug-var-dump' dir='ltr'><small>string</small> <font color='#cc0000'>'GET :'</font> <i>(length=5)</i>
</pre><pre class='xdebug-var-dump' dir='ltr'>
<b>array</b>
  'itemId' <font color='#888a85'>=&gt;</font> <small>string</small> <font color='#cc0000'>'0'</font> <i>(length=1)</i>
</pre>

Then if I click again I get the same alerts and output except that at the end I get 21<pre class='xdebug-var-dump'..... Next click produce the same except with 32<pre class.... at the end, etc.

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1 Answer

  1. Editorial Team

    Try defining the function for onreadystatechange event inline. Also, the textarea’s value is accessed using value, not innerHtml. The modified showNext() would be:

    function showNext(itemId){
    request=getRequest();
    if(request==null){
        return;
    }
    var url="index.php?itemId="+escape(itemId);
    request.open("GET",url,true);
    request.onreadystatechange= function(){
        if(request.readyState==4){
            if(request.status==200){
            document.getElementById('article').value=request.responseText;
            }
        }   
    }
    request.send(null);
}
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