Head Rush Ajax

104

Chapter 2

Under the Microscope:

So when exactly does the ready state of a request

change? Here’s a close-up look at the ready state

of a request, and how it changes as a request is

processed by a web server.

HTTP Ready States

getCustomerInfo() calls open()

on the request object, and

initializes the connection.

The JavaScript function

you assigned to the

onreadystatechange property is

run, and can use the server’s data.

0

Connection

uninitialized

var request = ...

<script>

var request...

function foo()

{

...

}

</script>

updatePage()

Web Page

JavaScript

This JavaScript function can

update the HTML page using the

response data from the server.

When the web page is

loaded, a new request

object is created.

<script>

var request...

function foo()

{

...

}

</script>

JavaScript

getCustomerInfo()

Here’s the request object’s

ready state, stored in the

readyState property.

This is the callback function that

you just learned about...

http ready states

Man, Break Neck pizza rocks. There’s

nothing like a breakfast of cold pizza, a

whipped latte from Starbuzz, and the

Webville Times to read.

<script>

var request...

function foo()

{

...

}

</script>

JavaScript

<script>

var request...

function foo()

{

...

}

</script>

Customer’s Phone Number

Customer’s Address

Customer’s Order

request.open(“GET”, url, true);

you’re on your way 4

105

ajax requests ...