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XML HTTP request

function callback_function(sData) {

//interpret data here

}

The callback function is passed the data retrieved from the HTTP request as its only argument,

sData

You are then free to do as you please with the result. In order to use the callback function, you must con-

sider a couple of details.

First, when using the XML HTTP request object to perform a GET, it’s easy to set up a callback function

by using an asynchronous request and calling the function when the

readyState

is equal to

Http.get = function (sURL, fnCallback) {

if (bXmlHttpSupport) {

var oRequest = new XMLHttpRequest();

oRequest.open(“get”, sURL, true);

oRequest.onreadystatechange = function () {

if (oRequest.readyState == 4) {

fnCallback(oRequest.responseText);

}

oRequest.send(null);

}

//...

};

This section of code uses JavaScript closures to allow the callback function,

fnCallback

, to be used in

the

onreadystatechange

event handler. Because

fnCallback

is just a function, it’s called like any

other function and passed the

responseText

of the request when

readyState

If there is no support for the XML HTTP request, you must check whether LiveConnect is enabled.

Unfortunately, no property or setting indicates whether LiveConnect can be used. The only way to tell is

to ensure that Java is enabled in the browser by using the

navigator.javaEnabled()

method and

determine whether the type of

java

and

java.net

are not undefined: