A coworker passed along this link from IBM which provides a nice series of tutorials on AJAX. The example below is a classic example of how to use the XMLHTTPRequest object while checking for different browser types and then using the server's response for something.
<script language="javascript" type="text/javascript">
var request = false;
try {
request = new XMLHttpRequest();
} catch (trymicrosoft) {
try {
request = new ActiveXObject("Msxml2.XMLHTTP");
} catch (othermicrosoft) {
try {
request = new ActiveXObject("Microsoft.XMLHTTP");
} catch (failed) {
request = false;
}
}
}
if (!request)
alert("Error initializing XMLHttpRequest!");
function getCustomerInfo() {
var phone = document.getElementById("phone").value;
var url = "/cgi-local/lookupCustomer.php?phone=" + escape(phone);
request.open("GET", url, true);
request.onreadystatechange = updatePage;
request.send(null);
}
function updatePage() {
if (request.readyState == 4) {
if (request.status == 200) {
var response = request.responseText.split("|");
document.getElementById("order").value = response[0];
document.getElementById("address").innerHTML = response[1].replace(/\n/g, "<br />");
} else if (request.status == 404) {
alert ("Requested URL is not found.");
} else if (request.status == 403) {
alert("Access denied.");
} else
alert("status is " + request.status);
}
}
</script>
<body>
<p><img src="breakneck-logo_4c.gif" alt="Break Neck Pizza" /></p>
<form action="POST">
<p>Enter your phone number:
<input type="text" size="14" name="phone" id="phone"
onChange="getCustomerInfo();" />
</p>
<p>Your order will be delivered to:</p>
<div id="address"></div>
<p>Type your order in here:</p>
<p><textarea name="order" rows="6" cols="50" id="order"></textarea></p>
<p><input type="submit" value="Order Pizza" id="submit" /></p>
</form>
</body>