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Using iframes

window.onload = function () {

parent.frames[0].handleResponse(

document.forms[“formResponse”].result.value);

};

</script>

</head>

<body>

<textarea name=”result”>This is some data coming from the

server.</textarea>

</form>

</body>

</html>

The important part about this window is the

onload

event handler, which calls the

handleResponse()

function from the first frame, passing in the value contained in the

element. It’s very

important that the

handleResponse()

function be called no matter what, even if there is an error, to

prevent the JavaScript in the main frame from hanging while waiting for a response.

The previous code shows data already inserted into the

for illustrative purposes; in

reality, this data would be output by some server-side logic.

When the

getServerInfo()

function is called in the main frame, the request is sent through the hidden

frame, and the data is passed back through the

handleResponse()

function and is displayed in an

alert. This is obviously a very simplistic example, but it illustrates the basic idea. The added bonus is

that this form of client-server communication works in any browser that supports framesets and

JavaScript (including older browsers like Netscape Navigator 4.x).

Using iframes

The hidden frame method evolved with the introduction of iframes into HTML. An

iframe

is a frame that

can be inserted anywhere in an HTML document, completely disconnected from any frameset. With this

innovation, developers changed the hidden frame method to create hidden iframes on the fly for the

purpose of communicating with the server.

To make use of iframes, you must make some changes to the

getServerInfo()

function:

var oHiddenFrame = null;

function getServerInfo() {

if (oHiddenFrame == null) {

oHiddenFrame = document.createElement(“iframe”);

oHiddenFrame.name = “hiddenFrame”;

oHiddenFrame.id = “hiddenFrame”;

oHiddenFrame.style.height = “0px”;

oHiddenFrame.style.width = “0px”;

oHiddenFrame.style.position = “absolute”;

oHiddenFrame.style.visibility = “hidden”;

document.body.appendChild(oHiddenFrame);

}

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Client-Server Communication

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