Head Rush Ajax

you’re on your way 4

107

ajax requests

Now that you’ve got getCustomerInfo() working, and the

browser knows to call updatePage() when the request’s ready state

changes, it’s time to write the callback function for the Break Neck

app. Let’s start out by checking that ready state, and making sure the

request has been completed before doing anything to the HTML.

Add a new function to your pizza.html le, called

updatePage(), and start with this code:

Checking the ready state

function updatePage() {

if (request.readyState == 4) {

/* Get the response from the server */

/* Update the order form */

}

}

You HAVE to make sure the

name of this function matches

up to the function name you

assigned to onreadystatechange

in getCustomerInfo().

You’ll write code to take care of both of

these things over the next few pages.

Remember, you

declared the

request variable

in your static

JavaScript, so any

function can use it.

This if statement makes sure that none of

the rest of the code runs unless the ready

state is “4”, which means the server’s nished,

and it’s safe to use the response data.

Q:

How does the server run the callback function when

the ready state changes? I didn’t think the server could call

JavaScript code that’s in an HTML page.

a: You’re right...it’s the browser that actually runs the callback

function. When the server is done with a request, it lets the

browser know. At that point, the ...