Introduction to Client-side Programming

The World Wide Web is a consortium of heterogeneous platforms.

When you are developing a web page using you are restricted to displaying a static page, you can’t take in user input, one can’t introduce interactivity using HTML.

HTML is basically static, the browser displays the text and graphics and waits for the user to click a link or fill in a form to return data to the server. Any dynamic behaviour is limited mainly to clicking a link or submitting a form to a server and receiving more static HTML.

When you want to introduce interactive features in your web pages, you can design programs that run either on the server side or the browser side (i.e. on the users' computer).

Look at today's typical Web-based form. You have designed a screen that asks users for their names and ages. A visitor to your page types his name properly, but types in "twenty-four" for his age instead of the number "24" (Even though the space on the screen is only three characters wide). This is what happens behind the scenes. When the user presses the Submit button on the form, his name and his age ("twenty-four") are sent over his modem across the country to a Web server, where there is a program a Server-side program) waiting for the input. Your program is expecting to get good data from the user and is ready to add it to the database. But instead, it gets this big string of alphabetic characters for the age. So your Web server creates an HTML page that asks the user to enter a valid age and sends this page back across the country to the user's browser. The user will hopefully complete the field correctly the second time and send the data back to your server again.

This whole process may take just a half a second, or several seconds, depending on the speed of the user's connection, the speed of the Net, Web server's load, and so on. This is not what you call a rich user experience--and what a waste of resources.

This is a typical process that happens millions of times a day, eats up bandwidth on the net, and uses your Web server CPU time to validate the input of a user. This validation could easily have been done on his local PC.

Moving these simple validation tasks from the server to the client is a simple task and is a big advantage of client-side scripting.

Client-side scripting is great for animating Web pages and performing local data validation and computations,

Client side programming is about extending the functionality of the browser.