Introduction to Programming the WWW I CMSC 10100-1 Winter 2003 Lecture 9

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

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”

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

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

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”;

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

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

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

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

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

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

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