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POcalling DB from javascript throwing error
 

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  1. POcalling DB from javascript throwing error
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    <p>i have a simple php page postArticle.php with two dropdown list with categories and subcategories and subcategories generates on the basis of categories.</p> <p>for generating subcategories i am using java script from which i am calling another php file(data.php)</p> <p>the code postarticle.php is</p> <pre><code>&lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt; &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt; &lt;head&gt; &lt;script type="text/javascript"&gt; function getSubCategories(l1,l2) { var response; var xmlHttp; if(l1.selectedIndex&gt;=1) { try{ var id=document.getElementById('listCategory').value; //alert("hello "+id); l2.disabled=false; if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari var xmlHttp=new XMLHttpRequest(); } else {// code for IE6, IE5 var xmlHttp=new ActiveXObject("Microsoft.XMLHTTP"); } //alert("hello 1"); xmlHttp.open("POST","data.php?q="+id,true); //alert("id passed is : " +id); xmlHttp.onreadystatechange = function(){ //alert("inside fn1"); if (xmlHttp.readyState == 4) { //alert("inside if fun"); //alert(xmlHttp.responseXML.getElementsByTagName("div")[0]); //alert("response text : "+xmlHttp.responseText); response=xmlHttp.responseText; } //alert("inside fn2"); } //alert("hello 3"); xmlHttp.send("data.jsp?q="+id); //alert('hello 4'); var resArray=new Array(); //alert('hello 5'); response=response.replace(/^\s+|\s+$/g,""); resArray=response.split("#"); //alert('hello 6'); //alert("response array : "+resArray); for(x in resArray) { //alert(resArray[x].substring(0, resArray[x].indexOf("*"))); //alert(resArray[x].substring(resArray[x].indexOf("*")+1)); if(resArray[x].substring(0, resArray[x].indexOf("*"))!=" " &amp;&amp; resArray[x].substring(resArray[x].indexOf("*")+1)!="") { var OptNew = document.createElement('option'); OptNew.text = resArray[x].substring(resArray[x].indexOf("*")+1); OptNew.value = resArray[x].substring(0, resArray[x].indexOf("*")); try { //for IE earlier than version 8 l2.add(OptNew,l2.options[null]); } catch (e) { l2.add(option,null); } } } }catch(e){alert(e.toString());} } else { return; } var newOpt = new Option(selText[i], selValues[i]); theSel.options[i] = newOpt; } &lt;/script&gt; &lt;meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /&gt; &lt;title&gt;Untitled Document&lt;/title&gt; &lt;/head&gt; &lt;body&gt; &lt;table border="1" width="100%"&gt; &lt;tr id="header" &gt; &lt;td height="30%" width="100%" colspan="3"&gt; &lt;?php include("Header.php"); ?&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr id="body"&gt; &lt;td height="65%" width="15%" valign="center"&gt; &lt;table width="100%"&gt; &lt;tr&gt;&lt;td&gt; &lt;?php include("LeftPanel.php"); ?&gt; &lt;/td&gt; &lt;/tr&gt; &lt;/table&gt; &lt;/td&gt; &lt;td height="65%" width="75%" valign="center"&gt; &lt;form method="post" action="PostArticle_Back.php"&gt; Title: &lt;input type="text" name="txtTitle" id="txtTitle"&gt; &lt;br&gt; Content : &lt;textarea id="txtContent" name="txtContent" rows="5" cols="50"&gt;&lt;/textarea&gt; &lt;br&gt; &lt;p&gt;select Category :&lt;/p&gt; &lt;select id="listCategory" name="listCategory" onchange="getSubCategories(listCategory,listSubCategory)"&gt; &lt;option value="0"&gt;Select Category&lt;/option&gt; &lt;?php $con=mysql_connect("localhost","root",""); if(!$con) { die('Could not connect: ' . mysql_error()); } mysql_select_db("articles_db",$con); $result = mysql_query("select CATEGORY_ID, CATEGORY_NAME from TBL_CATEGORIES"); while($row = mysql_fetch_array($result)) { ?&gt; &lt;option value="&lt;?php echo $row['CATEGORY_ID'] ; ?&gt;" &gt; &lt;?php echo $row['CATEGORY_NAME'] ; ?&gt; &lt;/option&gt; &lt;?php } ?&gt; &lt;/select&gt; &lt;br&gt; &lt;p&gt;select SubCategory :&lt;/p&gt; &lt;select id="listSubCategory" name="listSubCategory" disabled="true"&gt; &lt;option value="0"&gt;select Subcategory&lt;/option&gt; &lt;/select&gt;&lt;br&gt; &lt;input type="submit" value="Post Article"/&gt; &lt;/form&gt; &lt;/td&gt; &lt;td height="65%" width="10%" valign="center"&gt; Right panel &lt;/td&gt; &lt;/tr&gt; &lt;tr id="footer"&gt; &lt;td height="5%" colspan="3"&gt; Footer &lt;/td&gt; &lt;/tr&gt; &lt;/table&gt; &lt;/body&gt; &lt;/html&gt; </code></pre> <p>but it throws an error <strong>TypeError : undefined is null or not an object</strong></p> <p>the problem what i find till now is that the data.php is taking time to send response </p> <p>if(xmlHttp.readyState == 4) is taking time to execute.</p> <p>because when i add alert statements in between code it works fine.</p> <p>what i tried till now:</p> <ol> <li><p>i tried to add while loop outside if condition but broweser gives a warning : <strong>script is making your webpage slow</strong></p></li> <li><p>i tried to put the code(the code for adding repose to drop down list) in if(xmlHttp.readyState == 4) condition but it did not gave any response.</p></li> </ol>
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    1. COtry adding xmlHttp.status 200, status 200 means OK! `if(xmlHttp.readyState == 4 && xmlHttp.status == 200)` and "4" complete, all data downloaded
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