Head Rush Ajax

118

Chapter 2

So to get around the caching, we have to

change our request URL every time. But... if

we’re talking to the same script, and we’re

not sending in data in the Boards app, how

can we make the URL different?

The browser doesn’t care how the request URL

is different; it just cares that it’s different. So, we

can add a dummy parameter onto the request

URL, and give it a different value every time

we send the request. And, since we don’t want

to write a random number generator, or do any

extra work, we can just grab the current time (in

seconds), and add that to the request URL.

Let’s take a look at how we can x up

getBoardsSold() from Chapter 1:

Sometimes it takes a hack...

function getBoardsSold() {

createRequest();

var url = “getUpdatedBoardSales-ajax.php”;

url = url + “?dummy=” + new Date().getTime();

request.open(“GET”, url, true);

request.onreadystatechange = updatePage;

request.send(null);

}

Remember back in the

old days, when our

request object was

created in a function?

This rst line sets the

URL normally, and the

second line adds a dummy

value to the URL.

Our dummy

parameter has

the current time

as its value.

Now the request URL changes...

getUpdatedBoardSales-ajax.php?dummy=1139262723388

getUpdatedBoardSales-ajax.php?dummy=1139262774440

getUpdatedBoardSales-ajax.php?dummy=1139262797519

...because each time the request URL

is built, the time is slightly different.

Now, no ...