How Ajax Works
Ajax is not as complicated as it may seem at first. A request needs to be sent to the server, a service invoked, and data returned. However, instead of submitting a form and loading a new page with the response, Ajax handles all of this activity within the context of the same page.
A special object, either Microsoftâs ActiveXObject
or the more general XMLHttpRequest
, manages the asynchronous
communication between the server and the client. Asynchronous
means that the request is sent,
but the client doesnât have to stop, hold, and wait for the process to
finish; there is no twirly icon to signal working
while you twiddle your thumbs. Instead, the client provides a function
to be called when the state of the request changes. In this function,
this state is checked; then, based on its value, as well as the status
of the request, the data returned from the service is processed and
usually output to the page in some form.
To the web-page reader, all of this activity looks as if the processing is happening within the page, rather than through client/server interaction. The only indicator that server access is happening is if this information is specifically provided.
Now that weâve had the 10,000-foot view, letâs look first at an Ajax application, and then go through the individual pieces in the rest of the chapter.
Tip
Ajax does require a server-side component. Iâm using PHP for this book because PHP is probably one of the most common scripting languages used today. ...
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