Web Programming Step by Step

Lecture 16
Global DOM Objects; Events

Reading: 8.1; 9.1 - 9.2

Except where otherwise noted, the contents of this presentation are Copyright 2010 Marty Stepp and Jessica Miller.

Valid XHTML 1.1 Valid CSS!

8.1: Global DOM Objects

The six global DOM objects

Every Javascript program can refer to the following global objects:

document current HTML page and its content
history list of pages the user has visited
location URL of the current HTML page
navigator info about the web browser you are using
screen info about the screen area occupied by the browser
window the browser window

The window object

the entire browser window; the top-level object in DOM hierarchy

Popup windows with window.open

window.open("http://foo.com/bar.html", "My Foo Window",

The document object

the current web page and the elements inside it

The location object

the URL of the current web page

The navigator object

information about the web browser application

The screen object

information about the client's display screen

The history object

the list of sites the browser has visited in this window

9.2: Event-Handling

JavaScript events

abort blur change click dblclick error focus
keydown keypress keyup load mousedown mousemove mouseout
mouseover mouseup reset resize select submit unload

Attaching event handlers the Prototype way

element.onevent = function;
element.observe("event", function);
// call the playNewGame function when the Play button is clicked
$("play").observe("click", playNewGame);

The event object

function name(event) {
	// an event handler function ...
method / property name description
type what kind of event, such as "click" or "mousedown"
element() * the element on which the event occurred
stop() ** cancels an event
stopObserving() removes an event handler

Mouse events (9.2.2)

click user presses/releases mouse button on the element
dblclick user presses/releases mouse button twice on the element
mousedown user presses down mouse button on the element
mouseup user releases mouse button on the element
mouseover mouse cursor enters the element's box
mouseout mouse cursor exits the element's box
mousemove mouse cursor moves around within the element's box

Mouse event objects

The event passed to a mouse handler has these properties:

mouse event
property/method description
clientX, clientY coordinates in browser window
screenX, screenY coordinates in screen
offsetX, offsetY coordinates in element (non-standard)
pointerY() *
coordinates in entire web page
isLeftClick() ** true if left button was pressed

Mouse event example

<pre id="target">Move the mouse over me!</pre>
window.onload = function() {
	$("target").observe("mousemove", showCoords);

function showCoords(event) {
	$("target").innerHTML = 
		  "pointer: (" + event.pointerX() + ", " + event.pointerY() + ")\n"
		+ "screen : (" + event.screenX + ", " + event.screenY + ")\n"
		+ "client : (" + event.clientX + ", " + event.clientY + ")";
Move the mouse over me!

The keyword this (8.1.3)

this.fieldName                  // access field
this.fieldName = value;          // modify field

this.methodName(parameters);    // call method

Event handler binding

window.onload = function() {
	$("textbox").observe("mouseout", booyah);   // bound to text box here
	$("submit").observe("click", booyah);       // bound to submit button here

function booyah() {           // booyah knows what object it was called on
	this.value = "booyah";

Fixing redundant code with this

	<label><input type="radio" name="ducks" value="Huey"  /> Huey</label>
	<label><input type="radio" name="ducks" value="Dewey" /> Dewey</label>
	<label><input type="radio" name="ducks" value="Louie" /> Louie</label>
function processDucks() {
	if ($("huey").checked) {
		alert("Huey is checked!");
	} else if ($("dewey").checked) {
		alert("Dewey is checked!");
	} else {
		alert("Louie is checked!");
	alert(this.value + " is checked!");