HTML and CSS Reference
In-Depth Information
of the Web site in the browser's URL location box. The “request” is transmitted
to the server via Hypertext Transfer Protocol (HTTP). The Web server on the
other side accepts that request. If the request is for an HTML file, the Web
server responds by simply returning the file to the client's browser. The browser
will then render the HTML tags, format the page for display, and wait for
another request. If the page contains JavaScript tags, the JavaScript interpreter
will handle that code based on a user-initiated event such as clicking a button,
rolling a mouse over a link or image, or submitting a form. It is with JavaScript
that the page becomes interactive. JavaScript detects whatever is happening on
the page and responds. It handles fillout forms, feedback, animation, slide-
shows, and multimedia. It responds to a key press, a mouse moving over an
image, or a user submitting a form. It can read cookies and validate data. It can
dynamically change a cell in an HTML table, change the text in a paragraph, or
add a new bullet item to a list. But it doesn't do everything. It cannot close a
window it didn't open, query a database, update the value in a file upload field,
or write to files on a server. After the JavaScript interpreter has completed its
tasks, and the page has been fully rendered, another request can be made to the
server. Going back and forth between the browser and the server is known as
the Request/Response loop, the basis of how the Web works.
2. The cloud between the client side and the server side represents the network.
This can be a very large network such as the Internet consisting of millions
upon millions of computers, an intranet within an organization, or a wireless
network on a personal desktop computer or handheld device. The user doesn't
care how big or small the network is—it is totally transparent. The protocol
used to transfer documents to and from the server is called HTTP.
3. The server side includes an HTTP Web server such as Apache, Microsoft's IIS,
or lighttpd. Web servers are generic programs capable of accepting Web-based
requests and providing the response to them. In most cases, this response is
simply retrieving the file from server's local file system. With dynamic Web
sites, which require processing beyond the capabilities of JavaScript, such as
processing form information, sending e-mail, starting a session, or connecting
to a database, Web servers turn over the request for a specific file to an appro-
priate helper application. Web servers, such as Apache and Internet Informa-
tion Service (IIS) have a list of helper applications that process any specific
language. The helper application could be an external program, such as a
CGI/Perl script, or one built right into the server, such as ColdFusion, ASP.NET,
or a PHP script. For example, if the Web server sees a request for a PHP file, it
looks up what helper application is assigned to process PHP requests, turns
over the request to the PHP module, and waits until it gets the result back.
1.5 What Is Ajax?
Ajax stands for Asnychronous JavasScript and XML, a term that was coined by Jesse
James Garrett in 2005. Ajax is not new. It's been around since 1996, and is a technique
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