Head Rush Ajax

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Appendix II

ajax.js

You’ve seen this code plenty of times by now. This little bit of JavaScript takes care of

creating a request object, and makes sure that the object will work on all modern web

browsers, from Internet Explorer to Firefox to Opera. Get used to this code if you’re not

already... it’s the foundation of every Ajax application.

var request = null;

try {

request = new XMLHttpRequest();

} catch (trymicrosoft) {

try {

request = new ActiveXObject(“Msxml2.XMLHTTP”);

} catch (othermicrosoft) {

try {

request = new ActiveXObject(“Microsoft.XMLHTTP”);

} catch (failed) {

request = null;

}

}

}

if (request == null)

alert(“Error creating request object!”);

You’ll see a lot of code that uses false

here, instead of null, but that won’t work

on some versions of IE. Stick with null, and

your code will work on all platforms.

We put all this code in a le called ajax.js.

You can call it anything you like, as long as

you change your HTML <script> tag to refer

to the right lename.

Remember, you’ve got to

try XMLHttpRequest

for browsers like Opera

and Mozilla, and then

try ActiveXObject for

Internet Explorer.

OK, we admit it... this isn’t the most

robust way to handle errors. By now,

though, you’re ready to add some more

advanced error handling on your own.

Follow the code... things end up here

if all the different attempts at

creating a request object fail.

creating a request object