JavaScript Lessons
D. Baggs, Annapolis, MD - Last updated on February 28,2000

Here are my assignments
Exercises-examples

Week One: Introduction

JavaScript is a client-side language- the code resides within the Web page. It is a hybrid between a programming language and a markup language - the former because it provides a set of instructions, the latter because it is less strict.

Self-Review Questions
1. JavaScript is a compact, object-based scripting language which allows the viewer to interact.


2. JavaScript was invented by Netscape with Sun Microsystems


3. JavaScript is different from Java as follows:
   
   • Interpreted rather than compiled
   
   
   • Object-based, but no inheritance
   
   
   • Code integrated with and embedded in HTML
   
   
   • Variable data types not declared
   
   
   • Dynamic (vs. Static) binding - Object references checked at run-time
   
   
4. JavaScript may lead to ECMAScript (European Community Manufacturer's Association) and it can write a text-based cookie.


5. It does not access and control a user's computer.

First Script:
• Script tag is usually embedded in the HEAD tags and usually is seen as <script language="JavaScript">
• The HTML comment tags are used to hide the JavaScript from non-JS capable browsers.
• Closing comment tag includes two forward slashes and HTML.


Rules
1. Capitalization matters
2. Opening symbols require matching closing symbols.
3. Use Comments
4. Scripts are made up of statements with the following structure:
• Statement starts on its own line.
• The first item is a command
• Next is some information, like a value
• Last is a trailing semi-colon.
• Groups of statements make command blocks:
• Starts on it's own line with an open brace-{
• Next -one or more individual statements ending with semi-colon
  Good to indent.
• Last is closing brace -}

Objects:
    Things which have unique names. Similar to a noun.
Properties:
    Can modify objects and are like sub-objects.
Methods:
    What objects do Similar to a verb.
Dot Syntax:
    Used to put together objects, properties, and methods.

Values and Variables

Value

Piece of information - numbers and strings.

Value Types

Consist of number, string, boolean, null, object, and function.

Operators

Symbols that work with variables. Examples are math functions.

Review Questions:
1. Objects are things
2. Properties are characteristics which can modify objects
3. Methods are things objects can do - actions
4. Dot syntax puts together objects, prop's, meth's
5. Event handlers are actions visitors perform - commands
6. Values are information - numbers/strings
7. Variables contain values
8. Operators are symbols that work w/variables

Alerts, prompts and confirms are three methods of the window object.
They create predefined, popup types of dialogue objects within a window object.

Clicking OK in an alert box makes the box disappear.

A prompt box has a space for writing.

A confirm box has a question.

A function is a set of Java statements that perform a task.
It is made up of the word function followed by the name, parentheses,
and an open brace bracket, statements, and a closing brace bracket.

A window opened with HTML will give the same size as the main window. JavaScript gives more control over size and properties.

type=full window opens new window on entire desktop with only the title bar.

Popups can be invoked using graphic link by using img src tag

Without a check for recognition of images for navigation, a user wouldn't be able to go anywhere.
The mouseover event calls the image defined in over1, etc. list and creates a message in the status bar.
Onmouseout calls the image defined in off1, etc. list.
Preloading images helps because you have twice what you see at first.