Head Rush Ajax

88

Chapter 2

First, we declare a new variable to represent the request object,

so we can use that variable in the rest of our JavaScript.

Declare a request variable

Next, we dene a new function called createRequest().

The rst thing this function does is try and create a new

request object using the XMLHttpRequest type, which

works on almost all browsers except Internet Explorer:

Try and create XMLHttpRequest for non-Microsoft browsers

var request = null;

function createRequest() {

try {

request = new XMLHttpRequest();

} catch (trymicrosoft) {

// Try something different

// for Microsoft

// (check out step 3)

}

if (request == null)

alert(“Error creating XMLHttpRequest!”);

}

Remember, this variable is not declared

in a function... it’s just nested inside

pizza.html’s <script> tags.

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request

Supporting multiple browsers

At the end of all this, spit out an error

if the request variable is still null.

It’s time to break into this pre-assembled JavaScript, and gure out

exactly what’s going on. Let’s walk through exactly what each piece

of createRequest() does, step-by-step.

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XMLHttpRequest

Since this variable isn’t declared inside

a function, any of your JavaScript

functions can use it.

XMLHttpRequest works

on Safari, FireFox,

Mozilla, Opera, and most

non-Microsoft browsers.

If that fails,

let’s try

something else.

We want our request

variable t ...