Javascript, Java and more
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Making Web Pages "Interactive"
What sets web pages apart from just a printed page?
- motion
- sound effects
- the ability of the user to manipulate things on the screen
- animation and video
Java
Java is an object-oriented programming language developed by Sun Microsystems
Not related to JavaScript, which is a scripting language developed to run within an HTML document in a browser
Java Applets
A self-contained mini-executable program
Named with a .class suffix
Can be placed right on a web page like a graphic
Advantages
Platform independent
Download completely and run on the client-side
Compact and download quickly
Do not require a proprietary plug-in
Disadvantages
Browsers are temperamental in dealing with Java applets
Takes time for a browser to initialize Java
What can Java Applets Do?
Everything from simple animations to flight simulators
Java allows for computations on-the-fly
Other things they can do:
- utilities (calculators, clocks, calendars, etc)
- text effects (scrolling marquees, wiggling text, etc.)
- audio effects (digital "guitars", radio buttons, etc.)
- games
Where to Get Applets
Hire a programmer to do a customized applet
Visit Sun's Java site
Or Java Boutique
Adding an Applet to a Page
Download the .class file along with any associated image or audio files
Save the file in the same directory as the HTML file
Place on the web page using the <applet>….</applet> tags
JavaScript
A client-side scripting language
Placed directly in the HTML document
Syntax:
<SCRIPT LANGUAGE = "JavaScript">
Add the script here
</SCRIPT>
Basics of JavaScript
Simple output - the alert box
- output statements will have some string value to be shared with the user
Example:- Hello World
<HTML>
<SCRIPT>
alert("Hello World");
</SCRIPT>
</HTML>
Variables
Containers that hold some type of data (like a refrigerator container)
Characteristics of variables:
- name
- type
- initial value
Creating Variables
The var statement
- var userName = "Susan";
- alert(userName);
The = does not mean "equals" but means "gets" as the variable userName gets the value of "Susan"
We then output the variable userName value "Susan" in an alert message to the user
Input
Uses the prompt statement
Syntax:
variable = prompt(question)
Example:
userName = prompt ("What is your name?");
The answer from the user is stored in the variable userName which then could be sent back to the user using an alert message
alert ("Hello " + userName);
References for JavaScript Information
A good book for JavaScript information
JavaScript Bible by Danny Goodman
DHTML
Dynamic HTML - web pages that move, animate or respond to the user after downloading
Works in conjunction with:
- HTML 3.2
-JavaScript
-CSS
-Document Object Model (DOM)
Advantages to DHTML
Small file sizes
Supported by both major browser manufacturers
Will be a standard
No plug-in necessary
Does not require a Java Virtual Machine
Disadvantages
Only new browsers support DHTML
Netscape and Microsoft IE have different DHTML implementations
DHTML has a sharp learning curve
Unprotected source code
DOM
The Document Object Model exposes every element of an HTML page to a scripting language such as JavaScript.
DOM begins with a base object call the "window" which refers to the browser window
Within the window object is a document object
The document object refers to the HTML page and everything in it
JavaScript Example:
document.images["images_name"]