(JavaScript

What is JavaScript?

It is a scripting language created by Netscape Communication Corp.
It functions as a means of adding client-side features to web content without a great deal of programming

What JavaScript is NOT

JavaScript is not "Fat-Free Java" - it is not meant to be a scaled-down version of Java
It was not intended to be a replacement for CGI scripts
It DOES function as an outstanding way to enhance both

Compare and Contrast Java and JavaScript

JavaScript

JavaScript is a scripting language -- an extension of HTML
Interpreted (not compiled by client
Object-based. Code uses built-in extensible objects, but no classes or inheritance
Code integrated with, and embedded in HTML
Variable data types not declared (loose typing)
Dynamic binding. Object references checked at run time
Secure. Cannot write to hard disk

Java

Java is a programming language
Compiled on server before execution on client
Object-oriented. Applets consist of object classes with inheritance
Applets distinct from HTML (accessed from HTML pages)
Variable data types must be declared (strong typing)
Static binding. Object references must exist at compile time
Secure. Cannot write to hard disk

A Trivial Example of JavaScript

<html>
<head>
My first JavaScript!
</head>
<body>
<br>
This is a normal HTML document.
<br>
<script language = "Javascript">
document.write("This is JavaScript!")
</script>
<br>
Back in HTML again.
</body>
</html>

The output would be:

This is a normal HTML document
This is JavaScript!
Back in HTML again.

A script with a function and comments

<html>
<head>
<script language = "Javascript">
<!-- to hide script contents from old browsers
function square(i){
document.write("The call passed", i, "to the function.","<BR>)
return i * i
}

document.write("The function returned", square(5), ".")
// end hiding contents from old browsers -->
</script>
</head>
<body>
<br>
All done.
</body>
</html>

The output would be:

The call passed 5 to the function.
The function returned 25.
All done.

** Note on the previous example that the script was placed in HTML comments ...that is Code Hiding. It is used to ensure that your JavaScript code is not displayed by old browsers that do not recognize JavaScript.

Useful applications of JavaScript

Add functionality to an HTML document: one can add menus, windows, dialog boxes, buttons, etc.
Scripts can interact with objects within a web page such as forms, frames background color and many others.
Most useful: validating form input before it is submitted to a CGI script on the server.

On the horizon...

Sun and Netscape are currently working together so that the next release of JavaScript will be capable of interacting with Java applets, allowing several applets on one page to pool information and manipulate objects within the page such as forms.

Also See

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HelpNet was created by the 1995 incoming graduate class. It is only occasionally updated.	Department of Computer Science School of Engineering, University of Virginia 151 Engineer's Way, P.O. Box 400740 Charlottesville, Virginia 22904-4740 (434) 982-2200 Fax: (434) 982-2214	Web Comments: webteam@cs.virginia.edu Admissions Inquiries: inquiry@cs.virginia.edu Site directory, Other addresses Server statistics © Created by the CS Web Team