CSE3325 : Javascript, Part 3

In the previous lecture:

Javascript Syntax summary

In this lecture:

Working with JavaScript: objects, and events.

Reference:

Same as the previous lecture:

Flanagan, D. JavaScript: The Definitive Guide
2nd edn, O'Reilly & Associates, Inc.
Stein, L.D. How To Set Up and Maintain a Web Site
2nd edn, Addison Wesley 1997, Chpt10.
Goodman, D. Dynamic HTML: The Definitive Reference
O'Reilly & Associates, Inc.

It is essential that one or more of these texts, or some other reference (eg. the WWW) be consulted on this topic.
This page is a summary only of a few important JavaScript language features after Stein. It is not intended to be a comprehensive explanation of JavaScript.

Using JavaScript

Insert JavaScript code between <SCRIPT> and </SCRIPT> tags to be run as the document is loaded.
- NB: Functions embedded between these tags are only executed when called.
- Use the LANGUAGE attribute to explicitly set the scripting language to be used.
  
  <SCRIPT LANGUAGE="JavaScript">
  // ...JavaScript Src...
  </SCRIPT>
  
  or
  
  <SCRIPT LANGUAGE="JavaScript1.1">
  // ...JavaScript Source for Nav3.0+...
  </SCRIPT>
Use the <SCRIPT> and </SCRIPT> tags to reference a JavaScript .js file
- <SCRIPT LANGUAGE="JavaScript1.1" SRC="blah/blah/myJavaScriptFile.js">
  </SCRIPT>
- The JavaScript file is just JavaScript source! (No HTML <SCRIPT> or </SCRIPT> tags thankyou very much!)
- To make this work, the web server must be configured to export the JavaScript file with the correct MIME-type: "application/x-javascript".

Define event handlers

Event handlers are routines which are executed when the user (usually) performs some action, for example clicking on a button or selecting a text entry box.
The routine daisy discussed in a previous lecture was an example of an event handler. (It was called when the Panic Button was clicked).

Event handlers may be attached to objects defined by HTML, through the addition of new tag attributes introduced for this purpose.

Object	Supported Event Handlers
Area	onClick() onMouseOut() onMouseOver()
Button	onBlur() onClick() onFocus()
Checkbox	onBlur() onClick() onFocus()
FileUpload	onBlur() onChange() onFocus()
Form	onReset() onSubmit()
Frame	onLoad() onUnload()
Image	onAbort() onError() onLoad()
Link	onClick() onMouseOut() onMouseOver()
Radio	onBlur() onClick() onFocus()
Reset	onBlur() onClick() onFocus()
Select	onBlur() onChange() onFocus()
Submit	onBlur() onClick() onFocus()
Text	onBlur() onChange() onFocus()
Textarea	onBlur() onChange() onFocus()
Window	onBlur() onError() onFocus() onLoad() onUnload()

Define Timer Events
- Events maybe triggered at timeouts.
- Call setTimeout() to specify that a timer event will occur after a specified number of milliseconds have elapsed.
- setTimeout("closePodBayDoorsHAL();", 10000) // Call routine in 10 sec.
- To make a timeout event recur (as you'd do to create an animation)...
  
  function animate() { changeImage(); setTimeout("animate();", 500); }
- Timeouts can be cancelled: clearTimeout()

var X = setTimeout("doSomething();", 100);
var Y = setTimeout("doSomethingElse();", 105);

clearTimeout(X); // clear a specific timer

JavaScript Windows

JavaScript is intended largely for manipulating the contents of the browser.
The currently active browser window is represented in JavaScript by a window object. This is the object which is implicitly accessed when a window event handler is used. (Such as the alert handler)

alert("Danger Will Robinson!");
You can explicitly access the window object through a reference to it called window or self. These are actually properties of the real window object (which has no name).

window.alert("Danger Will Robinson!");

Window objects accessible properties...

Property	Description
defaultStatus	The default text displayed in the browser status bar
status	The transient text displayed in the browser status bar
history	The array of visited URL's
location	The window's URL
frames	The array of frames in the current window
name	The window's name
document	The document contained within the window

JavaScript Object Hierarchy

Beneath the JavaScript window object is a hierarchy of other objects, each with their own properties and methods.
Each object is a property of its container.
If an object has a name (eg. a form may have a name) this object may be referred to by its name.
We will meet this hierarchy again when we discuss the (Document Object Model) DOM of which it and JavaScript are a part.

JavaScript Examples

These simple examples illustrate some of the ways JavaScript can be used. From simple building blocks, medium programs can be built for all kinds of purposes.

Move the mouse over this link and look down at the status bar!
Let's go...
Try this wonderful link back to the top of the page so that you can read all this stuff again... but not before being asked if you really want to do so!
The current window location can be found using JavaScript and written into the document source as it loads! (As can a lot of other stuff actually.)
- The current location is:
- The current document protocol is:
- The current host is:
- The current document path is:
Let's go...

What's so interesting about that?
- Want to see the source code Dave?
- use of prompt() to fetch a URL
- window.open()
- onLoad()
- fetching the current date and time
- setTimeout()
- use of new Array()
- document image source access
- animation
- setting text entry box value
- window.close()

This lecture's key point(s):

JavaScript event model
Document Object Model (more on this later)
Manipulating Windows

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