XML fetching using javascript

This code wont execute. I think there is something wrong with the xhttp.send() function. Because the alert function before it executes but the alert function after it doesn't execute:

<html>
<head>
    <title>PAGE OUTPUT</title>
    <script type="text/javascript">
    function aa()
    {   
        var xhttp;
        alert("hi welcome"); 
        if(window.XMLHttpRequest)
        {
            xhttp=new XMLHttpRequest();
            alert("hi");
        }
        else
        {
            xhttp=new ActiveXObject("Microsoft.XMLHTTP");
        }
        xhttp.open("GET","vehicle.xml",false);
        alert("OPEN EXECUTED");
        xhttp.send();
        alert("SEND EXECUTED");
        xmlDoc=xhttp.responseXML;
        alert("HI I HAVE REACHED OVER HERE");
        var vehicle=xmlDoc.documentElement;
        var car=vehicle.firstChild.nodeValue;
        var price=car.firstChild.nodeValue;
        alert(price);
    }
    </script> 
</head>
<body>
<center><input type="submit" onclick="aa()"></center>
</body>

Solution

You'd better to check if the URL is like file:///path/to/file the browser will fail to send any XHR from the page, for security reasons (nowadays that seems unreasonable).

You should launch a server for this case, and visit that page in http://localhost/path/to/file. The easiest way I know is to launch a Python SimpleHTTPServer. You might install python yourself if you are using MS Windows, or it will be available in Mac/any Linux distributions. Then follow these steps

launch a terminal (on MS Windows it's called a command line prompt, using Win+R then type cmd to launch one)
cd to the path where the files locate
execute python -m SimpleHTTPServer
visit http://localhost:8000/html_file in your browser
click on that button as usual

Now you will see those alerts. Additionally, you might have to change xmlDoc=xhttp.responseXML to xmlDoc = xhttp.responseText if necessary.

Then try jQuery, that's much easier for ajax.