Ajax调用以获取数据

Dear I want to get Variable Value form PHP Value, and I want to write an ajax call in Java Script, tags, How it is possible, I want to get Value from get_result.php file, and I have following code in get_result.php:

<?php
echo $val="abc";
?>

and I wrote follwing code in another file named ajax.php:

<script>
        if (window.XMLHttpRequest)
        {
            xmlhttp=new XMLHttpRequest();
        }
        else
        {
            xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        }

        var url="<?php echo "get_result.php"; ?>";
        xmlhttp.open("GET", url, false);
        xmlhttp.send(null);
        var ok xmlhttp.responseText;
        alert(ok);
</script>

is there any bug and Where? I want to get value from get_result.php file and show this value in an Alert;

You can use jQuery. but for your code, you didn't assign the response

 <script>
            if (window.XMLHttpRequest)
            {
                xmlhttp=new XMLHttpRequest();
            }
            else
            {
                xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
            }

            var url="get_result.php";
            xmlhttp.open("GET", url, false);
            xmlhttp.send(null);
            var ok = xmlhttp.responseText;
            alert(ok);

The below code will help you in returning the value from the php page

   <script>
    function myfun()
    {
       var xmlhttp;
       if (window.XMLHttpRequest)
       {// code for IE7+, Firefox, Chrome, Opera, Safari
           xmlhttp=new XMLHttpRequest();
       }
       else
       {// code for IE6, IE5
          xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
       }
        xmlhttp.onreadystatechange=function()
       {
          if (xmlhttp.readyState==4 && xmlhttp.status==200)
          {
            var demo=xmlhttp.responseText;
            alert(demo);
          }
       }
            xmlhttp.open("GET","result.php",true);
            xmlhttp.send();
   }
  </script>

body

<body>
    <input type="button" onclick="myfun();"/>
</body>