Head Rush Ajax

16

Chapter 1

Let’s get back to updating Katie’s web report. First up, you need a function that creates

a new object to make requests to the server. This turns out to be a bit tricky, because

different browsers have different ways of creating this object. To help you out, we’ve

written some “pre-assembled” JavaScript for you. Whenever you see the logo,

it means you’ll have to take some code on faith, like this code below that creates an object

to make requests to the server. Trust us though—you’ll learn all about this code in more

detail in the chapters to come. For now, just type it in and see what it can do.

Pre-Assembled

JavaScript

n

n

Pre-Assembled

JavaScript

var request = null;

function createRequest() {

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!”);

}

Pre-Assembled

JavaScript

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Step 1: Creating a request object

This line tries to create a new

request object.

These two lines try and create the

request object, too, but in a way that

works on Internet Explorer.

This is the type of the

request object.

...and we can spit out an error

message to users with JavaScript’s

alert() function.

Here’s a variable to hold the request object.

If something ...