XMLHttp : Step 1 - Sanjeetosphere - Site Home

What is XMLHttpRequest?

- It is an API that is used by JavaScript and some other scripting languages to transfer data (XML/plain text) "to-and-from" a web server over HTTP.
- You can make a call from an html page also. In the following example we are not using any aspx page. Its plain simple htm with javascript.
- The point to note is: XMLHttpRequest is used by client side scripting engines to call server side methods. Your client needs to be capable enough to handle responses delivered by the request.
- The communication between client and server happens over a separate channel, and its the underlying concept behind AJAX.
- Practically, this simply means that you don't have to refresh the page in order to get "some" data. You are performing a partial page update.
- In Internet Explorer 6 and earlier, XMLHTTP was implemented as an ActiveX object provided by Microsoft XML (MSXML). Beginning with Internet Explorer 7, XMLHTTP is also exposed as a native scripting object.
- Internet Explorer 7 still supports the legacy implementation of XMLHTTP alongside the new native object, so pages currently using the ActiveX control do not need to be rewritten. However, it is much more efficient to create the native scriptable object than an ActiveX object. This is especially beneficial to those AJAX applications that create a new XMLHTTP object for each request.
- In the following example we are not calling any server side code that implements business logic, instead we are fetching the text response from http://www.microsoft.com. We will discuss how to consume Webservices directly from a browser with XMLHttpRequest without using AJAX.

What options can we use to instantiate an XMLHttpRequest object?
- There are chances that XMLHttp may be disabled on a domain level. We need to take this into account.
if(window.XMLHttpRequest) returns false
> Its disabled! but we can use "var xmlRequest = new ActiveXObject('MSXML2.XMLHTTP.3.0');" to instantiate
> You are not using IE 7, so you need to use: var xmlRequest = new ActiveXObject('MSXML2.XMLHTTP.3.0');

Prior to IE 7 you required the following to use XMLHttp:
var xmlRequest = new ActiveXObject("Microsoft.XMLHTTP");

However with IE 7 you can use the following pice of code:
var xmlRequest = new XMLHttpRequest();

var xmlRequest = new ActiveXObject("Microsoft.XMLHTTP");

function OnComplete(){
    var spn = document.getElementById("spn");
    switch(xmlRequest.readyState){
    case 1:
        spn.innerHTML = "connection opened.";
        break;
    case 2:
        spn.innerHTML += "<br>GET request sent.";
        break;
    case 3:
        spn.innerHTML += "<br>recieving data...<br>";
        break;
    case 4:
        spn.innerHTML += xmlRequest.responseText;
     alert("Length of response = " + xmlRequest.responseText.length);
     spn.innerHTML += "complete.";
        break;
    }
}

function hell(){
    xmlRequest.onreadystatechange = OnComplete;
    xmlRequest.open("GET", "http://www.microsoft.com", true);
    try{
     alert("about to send");
     xmlRequest.send();
     }
    catch(e){
     alert(e.message);
        }
}
</script>

XMLHttpRequest Object
http://msdn.microsoft.com/library/default.asp?url=/workshop/author/dhtml/reference/objects/obj_xmlhttprequest.asp