Ajax example
READYSTATE
The readyState property indicates the current state of an Ajax request. Its value is numerical:
- 0 Uninitialized. The open method hasn’t been called yet.
- 1 Loading. The open method has been called, but the send method hasn’t.
- 2 Loaded. The send method has been called. The request has begun
- 3 Interactive. The server is in the process of sending a response.
- 4 Complete. The server has finished sending a response.
STATUS
- I’m sure you’re familiar with the 404 status code, which translates to “Not Found.”
- Some other codes are 403 for “Forbidden,” and 500 for “Internal Server Error.”
- The most common status code is 200, which means “OK.”
- A value of 304 translates as “Not Modified.” The server sometimes returns this response if a browser performs what’s known as a conditional GET request. The Opera browser uses conditional GET requests. In this situation, the server may return a response of 304, indicating that the document hasn’t changed since it was last requested, so the browser can safely use a cached version.
- if 0, means ok, and the request url is local.
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title>Using XMLHttpRequest</title>
<script type="text/javascript" src="ajaxtest.js"></script>
</head>
<body>
<p>
<a href="message.txt" onclick="grabFile(this.href); return false;">
Click here to see the contents of a text file
</a>
</p>
</body>
</html>
JavaScript Codes
function getHTTPObject() {
var xhr = false;
if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
} else if (window.ActiveXObject) {
try {
xhr = new ActiveXObject("Msxml2.XMLHTTP");
} catch(e) {
try {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
} catch(e) {
xhr = false;
}
}
}
return xhr;
}
function grabFile(file) {
var request = getHTTPObject();
if (request) {
request.onreadystatechange = function() {
displayResponse(request);
};
request.open("GET", file, true);
request.send(null);
}
}
function displayResponse(request) {
if (request.readyState == 4) {
if (request.status == 200 || request.status == 304) {
alert(request.responseText);
}
}
}
