Subject: Advanced Internet Technology

Topic: RIA and Mashup

Difficulty: Medium

Usage characteristics of JavaScript

• Display messages to the user, either as part of a web page or in alert boxes.

• Animate images or create images that change when you move the mouse over them.(rollovers)

• To trap events such as moving the mouse over a certain area of the screen.

• Request information from a server and display as needed, without reloading the whole page(AJAX)

• Show or hide content based on user interaction

• Use javascript libraries or frameworks to more easily accomplish common scripting tasks

• Detect the browser in use and display different content for different browsers.

• Detect installed plug-ins and notify the user if a plug in is required.

• As a scripting language to handle user events, like clicking on a form element. You can add dynamic mechanisms to your page that would have previously required CGI scripts. For example, you can display fonts in a larger or smaller type style. In this case, the browser’s JavaScript interpreter provides this functionality.

• JavaScript can also validate user input in a form before sending data to the server, acting as a buffer between Web servers and clients.

  • For example, if you have a form that requests an email address, you can check to see if the cell contains an @ sign or some text data before transferring the data to the server. In JavaScript, because the interpreter runs at the browser, all validation is done at the client. This acts as a buffer for the Web server by off-loading processing tasks. With a CGI script (such as PERL), data must go back and forth between client and Web server.

• You can also use JavaScript to identify a user and greet them when they access your Web site.

  • For example, when user Ryan accesses your Web site, you can display a message such as “Good Morning Ryan.” As a downloadable computation engine. The JavaScript interpreter can perform calculations at the client. Many Web sites have implemented calculators and tax calculation forms using JavaScript. (In a Perl script, data you enter must be sent to the Web server, computed, and the result returned to the client.)