Main Page

getServerInfo

setTimeout(function () {
frames[“hiddenFrame”].location.href = “HiddenFrameExampleCom2.htm”;
}, 10);
}
The first change is the addition of a global variable names
oHiddenFrame
. Because the same frame can
be used repeatedly for requests, there’s no reason to keep creating new iframes for each request. Instead,
this global variable holds a reference to the iframe when it’s created. When
getServerInfo()
is called,
it first checks to see if an iframe already exists by checking the value of
oHiddenFrame
. If it doesn’t exist,
the frame is created using the DOM
createElement()
method.
Creating the iframe using the DOM is very specific. Both the
name
and
id
attribute must be set to equal
“hiddenFrame”
in order for this to work in most browsers (some require
name
to be set, others require
id
). Next, the appearance of the frame is specified to have a height and width of
0
, an absolute position,
and visibility set to
“hidden”
. All these changes are necessary to ensure that this new addition to the
document doesn’t disrupt the display. Lastly, the iframe is added to the document body.
When the iframe has been created and added, it takes most browsers (notably Mozilla and Opera) a cou-
ple of milliseconds to recognize it as a new frame in the
frames
collection. To take this into account, the
setTimeout()
function is used to create a wait of 10 milliseconds before the request is sent. By the time
the request executes, the browsers recognizes the new frame, and it’s sent off without a hitch.
The only modification necessary to the page providing the response is to use
parent
instead of
parent.frames[0]
to call
handleResponse()
:
<html>
<head>
<title>Hidden Frame Example (Response)</title>
<script type=”text/javascript”>
window.onload = function () {
parent.handleResponse(document.forms[“formResponse”].result.value);
};
</script>
</head>
<body>
<form name=”formResponse”>
<textarea name=”result”>This is some data coming from the
server.</textarea>
</form>
</body>
</html>
Now calling
getServerInfo()
has the exact same effect as the previous example using the traditional
hidden frame technique. This technique requires, of course, that the browser support iframes in the first
place, which leaves older browsers like Netscape Navigator 4.x out of the loop.
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