{
     "firstName": "John",
     "lastName": "Smith",
     "address": {
         "streetAddress": "21 2nd Street",
         "city": "New York",
         "state": "NY",
         "postalCode": 10021
     },
     "phoneNumbers": [
         "212 555-1234",
         "646 555-4567"
     ]
 }

var the_object;
var http_request = new XMLHttpRequest();
http_request.open( "GET", url, true );
http_request.send(null);
http_request.onreadystatechange = function () {
    if ( http_request.readyState == 4 ) {
        if ( http_request.status == 200 ) {
            the_object = eval( "(" + http_request.responseText + ")" );
        } else {
            alert( "There was a problem with the URL." );
        }
        http_request = null;
    }
};

var req = new XMLHttpRequest();   
req.open('GET', url, true);   
req.onreadystatechange = function (aEvt) {   
  if (req.readyState == 4) {   
     if(req.status == 200)   
      the_object = eval ( “(“ + req.responseText+”)” );   
     else  
      dump("Error loading page\n");   
  }   
};   
req.send(null);  

var req = new XMLHttpRequest();   
req.open('GET', url, true);   
req.onreadystatechange = function (aEvt) {   
  if (req.readyState == 4) {   
     if(req.status == 200)   
      the_object = eval ( “(“ + req.responseText+”)” );   
     else  
      dump("Error loading page\n");   
  }   
};   
req.send(null);  

<script language="javascript" type="text/javascript">
  function GetJson(url) {
    // Create xmlhttprequest object
    var xmlhttp = null;
    if (window.XMLHttpRequest) {
      xmlhttp = new XMLHttpRequest();
      //make sure that Browser supports overrideMimeType
      if (typeof xmlhttp.overrideMimeType != 'undefined') {
        xmlhttp.overrideMimeType('text/xml');
      }
    }
    else if (window.ActiveXObject) {
      xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }
    else {
      alert('Perhaps your browser does not support xmlhttprequests?');
    }
    // Create an HTTP GET request
    xmlhttp.open('GET', url, true);
    // Set the callback function
    xmlhttp.onreadystatechange = function() {
      if (xmlhttp.readyState == 4){
        if (xmlhttp.status == 200) {
          var json = xmlhttp.responseText;
          the_object = eval(json);
        else {
          //error
        }
      };
    // Make the actual request
    xmlhttp.send(null);
  }
</script>

<script src="../../Scripts/MicrosoftAjax.js" type="text/javascript"></script>

<script language="javascript" type="text/javascript">
    function GetJson() {
        var request = new Sys.Net.WebRequest();
        request.get_headers()['Content-Type'] = 'application/json; charset=utf-8';
        request.set_url('/test.json');

        request.add_completed(Function.createDelegate(null, DisplayArtists));
        request.invoke();
    }

    function DisplayArtists(executor) {
        if (executor.get_responseAvailable()) {
            var jsonText = executor.get_responseData();
            var the_object = Sys.Serialization.JavaScriptSerializer.deserialize(jsonText);

            $get("divOutput").innerHTML = myArray.length;
        }
    }
</script>