DHTML

What is DHTML?

DHTML is the art of making HTML pages dynamic!

Dynamic HTML or DHTML is a term used for a collection of technologies, used together to create interactive and animated web sites by using a combination of static markup language (such as HTML), a client-side scripting language (such as JavaScript), the presentation definition language (Cascading Style Sheets).

Client-side scripting

Client-side scripting generally refers to the class of computer programs on the web that are executed client-side, by the user's web browser, instead of server-side (on the web server). This type of computer programming is an important part of the Dynamic HTML (DHTML) concept, enabling web pages to be scripted; that is, to have different and changing content depending on user input, environmental conditions (such as the time of day), or other variables.

Server-side scripting

Server-side scripting is a web server technology in which a user's request is fulfilled by running a script directly on the web server to generate dynamic HTML pages. It is usually used to provide interactive web sites that interface to databases or other data stores. This is different from client-side scripting where scripts are run by the viewing web browser, usually in JavaScript. The primary advantage to server-side scripting is the ability to highly customize the response based on the user's requirements, access rights, or queries into data stores.

What Is JavaScript?

JavaScript is the premier client-side scripting language used today on the Web. It’s widely used in tasks ranging from the validation of form data to the creation of complex user interfaces. JavaScript lets you build interactions between page content, the state of the browser, and the actions of the user.

Designed for Simple, Small Programs
JavaScript is well suited to implementing simple, small programs such as unit conversion calculator between miles and kilometers or pounds and kilograms. These tasks can be easily written and performed at acceptable speeds with JavaScript and would be easily integrated into a Web page.

Designed for Programming User Events
Because of the way in which JavaScript is integrated into the browser and can interact directly with HTML pages, JavaScript makes it possible to program responses to user events such as mouse clicks and data entry in forms.
For instance, a JavaScript script could be used to implement a simple help system. Whenever the user points at a button or a link on the page, a helpful and informative message can be displayed in the status bar at the bottom of the browser window.
This adds interactivity to Web pages, makes forms dynamic, and can decrease the bandwidth requirements and server load incurred.
Easy Debugging and Testing
Like other scripting languages, JavaScript eases development and trouble-shooting because it is not compiled. It is easy to test program code, look at the results, make changes, and test it again without the overhead and delay of compiling.

Versions of JavaScript
Version Description
JavaScript 1.0 The original version of the language. It was buggy and is now essentially obsolete. Implemented by Netscape 2.
JavaScript 1.1 Introduced a true Array object; most serious bugs resolved. Implemented by Netscape 3.
JavaScript 1.2 Introduced the switch statement, regular expressions, and a number of other features. Almost compliant with ECMA v1, but has some incompatibilities. Implemented by Netscape 4.
JavaScript 1.3 Fixed incompatibilities of JavaScript 1.2. Compliant with ECMA v1. Implemented by Netscape 4.5.
JavaScript 1.4 Implemented only in Netscape server products.
JavaScript 1.5 Introduced exception handling. Compliant with ECMA v3. Implemented by Mozilla and Netscape 6.
JScript 1.0 Roughly equivalent to JavaScript 1.0. Implemented by early releases of IE 3.
JScript 2.0 Roughly equivalent to JavaScript 1.1. Implemented by later releases of IE 3.
JScript 3.0 Roughly equivalent to JavaScript 1.3. Compliant with ECMA v1. Implemented by IE 4.
JScript 4.0 Not implemented by any web browser.
JScript 5.0 Supported exception handling. Partially compliant with ECMA v3. Implemented by IE 5.
JScript 5.5 Roughly equivalent to JavaScript 1.5. Fully compliant with ECMA v3. Implemented by IE 5.5 and IE 6. (IE 6 actually implements JScript 5.6, but 5.6 is not different from 5.5 in any way that is relevant to client-side JavaScript programmers.)
ECMA v1 The first standard version of the language. Standardized the basic features of JavaScript 1.1 and added a few new features. Did not standardize the switch statement or regular expression support. Conformant implementations are JavaScript 1.3 and JScript 3.0.
ECMA v2 A maintenance release of the standard that included clarifications but defined no new features.
ECMA v3 Standardized the switch statement, regular expressions, and exception handling. Conformant implementations are JavaScript 1.5 and Jscript 5.5.

Characteristics of JavaScript
1. Written using the Unicode character set.
2. Case-sensitive language.
3. JavaScript ignores spaces, tabs, and new lines that appear between tokens in programs, except those that are part of string or regular expression literals.
4. Simple statements in JavaScript are generally followed by semicolons (;), just as they are in C, C++, and Java.
5. JavaScript, like Java, supports both C++ and C-style comments
Ex. //  for single line comment
/* (text here) */  for multiple line comment