1. Introduction to Programming the WWW I
CMSC
Winter 2003
Lecture 9

2. Javascript Scripting language Started in 1995 - Netscape 2.0
Interpreted by browser
Interacts with Web pages
Started in Netscape 2.0
Microsoft followed suit
Long wranglings over standardizing it across browsers

3. What’s an object? Properties (have values) Abilities (methods)
can be accessed, set, etc
Abilities (methods)
Everything in the Web page is modelled by an “object”

4. Some sample Javascript
See examples from Chapter 1 of JS
Events: respond to user action
Send messages, get input form user

5. More Javascript
Variables: like “x” in algebra -- a name that stands for some other value
var myColor = “pink”;
window.document.bgColor = myColor;

6. Arrays An array is a collection of variables in some particular order:
var mycolors = new Array();
mycolors[0] = “red”;
mycolors[1] = “pink”;
mycolors[2] = “blue”;

7. Methods Dogs bark, cats pur, cars slow down
document.write(“Hello world!”)
Lots of predefined methods for manipulating Web pages, we’ll also learn how to define our own

8. Assignment & Comparison
You can change the values of variables:
mynumber = 42;
mynumber += 37;
mynumber -= 28;

9. Comparison 39 == 30 + 9; // True 39 >= 39; // True 2 != 2 // False

10. Functions
You can write functions to perform specific tasks where the input might be different:
Listing 1.3 in JS book

11. The DOM
A hierarchical model to represent the objects created by a Web browser
document.getElementById();

12. DHTML DHTML (Dynamic HTML)
Style sheets for color, layout, positioning
Javascript to update these things
Every object has a “style” property
Requires learning some about programming and a lot about Web pages
Example: Hot air balloon

13. What’s on the horizon: Dynamically modifying page content/appearance
rollovers
style changes
Dynamic visibility
sliding, drop down menus
text popups