Slide 2.31: HTML URLs and URL encoding

HTML URLs and URL Encoding

URL—Uniform Resource Locator
A URL is used to address a document (or other data) on the World Wide Web. A web address follows these syntax rules:

       scheme://host.domain:port/path/filename

scheme: defines the type of Internet service, e.g., http, ftp, and mailto.
host: defines the domain host (the default host for http is www).
domain: defines the Internet domain name, like w3schools.com.
:port: defines the port number at the host, e.g., 80, the default number.
path: defines a path at the server.
filename: defines the name of a document/resource.

URL Encoding
URL encoding converts characters into a format that can be transmitted over the Internet. URLs can only be sent over the Internet using the ASCII character-set. Since URLs often contain characters outside the ASCII set, the URL has to be converted into a valid ASCII format. URL encoding replaces non ASCII characters with a ‘%’ followed by two hexadecimal digits. For example, URLs cannot contain spaces. URL encoding normally replaces a space with a + sign. If you click the “Submit” button above, the browser will URL encode the input before it is sent to the server. A page at the server will display the received input. Some of the URL-encodings are listed as follows:

Character	URL-Encoding	Character	URL-Encoding	Character	URL-Encoding
@	%40	#	%23	$	%24
%	%25	&	%26	'	%27
<	%3C	=	%3D	?	%3F

Demonstration
The following demonstration shows how the HTML script is displayed on the Web.


<html> <head> <script type="text/javascript"> function show_alert( ) { alert( "Hello! I am an alert box!" ); } </script> <title>HTML Working Area</title> </head> <body> <input type="button" onclick="show_alert( )" value="Show alert box" /> </body> </html>