Head Rush Ajax

you’re on your way 4

187

asynchronous applications

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Request Object

The same request object sends

another request to the coffee

maker for Bob’s order.

Make Bob a medium latte using

the second coffee maker

coffeemaker.php

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Now enter another order, for Bob. Bob

wants a medium latte. Click “Order

Coffee”, and Bob’s order should start

brewing on the second coffee maker.

The same request object is

used to send the request

for Bob’s coffee order.

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Request Object

But what about Jim’s order?

Do you see the problem? Jim’s order is still brewing, but now there’s

no request object attached to that request! The request for Bob’s order

overwrote the information in the request object related to Jim’s order:

Bob’s order

Jim’s order

There’s no request object set up

to indicate a callback to run or

receive a server’s response from

the browser when the server

nishes with Jim’s order.

Bob’s order is set up normally. The

request object will tell the browser

what callback function to run, and the

callback can get the server’s response

from the request object.

A request object can be

used to make multiple

requests, but can only keep

track of one response from

the server at a time.

The connection between the

request object and Jim’s order

was overwritten when Bob

placed his order.

4

Bob’s order will

nish normally,

but Jim’s order ...