Hi,i am beginner with chrome extension.There is simple problem. There is the code in my extension,but it do not work.I don't know how to figure it out. In my extension, i used a xml file to stroe some data.There is the code in my background.html,but it do not work
    <!DOCTYPE html>
<html>
<head>
</head>
<body>
<script>
function loadXmlFile(){
   var xmlDom = null;
   var xmlhttp = new XMLHttpRequest();
       if( xmlhttp ){
               xmlhttp.onreadystatechange = function(){
                       if( xmlhttp.readyState == 4 ){
                            if( xmlhttp.status == 200 ){
                                       xmlDom = xmlhttp.responseXML;
                               }
                       }
               }
               xmlhttp.open( "GET",chrome.extension.getURL("/xml/123.xml"),true);
               xmlhttp.send( null );
       }
       return xmlDom;
}
var xmlDom = loadXmlFile();
var s = xmlDom.getElementsByTagName( "to" );
alert( s[0].nodeType );
</script>
</body>
</html>
I used developer tools to debug,but it says " Cannot call method 'getElementsByTagName' of null"... who can help me?