JavaScript

JavaScript Basics &
HTML DOM

Sang Shin
Java Technology Architect
Sun Microsystems, Inc.
sang.shin@sun.com
www.javapassion.com

Disclaimer & Acknowledgments
• Even though Sang Shin is a full-time employee of
Sun Microsystems, the contents here are created as
his own personal endeavor and thus does not
necessarily reflect any official stance of Sun
Microsystems on any particular technology
• Acknowledgments
> The contents of this presentation was created from JavaScript
tutorial from www.w3cschools.com

2

Topics

• What is and Why JavaScript?
• How and Where do you place JavaScript code?
• JavaScript language
• JavaScript functions
• JavaScript events
• JavaScript objects
• JavaScript HTML DOM objects
• Closure (need to be added)
3

What is JavaScript?

• Was designed to add interactivity to HTML pages
• Is a scripting language (a scripting language is a
lightweight programming language)
• JavaScript code is usually embedded directly into
HTML pages
• JavaScript is an interpreted language (means that
scripts execute without preliminary compilation)

5

What can a JavaScript do?

• JavaScript gives HTML designers a programming
tool
• JavaScript can put dynamic text into an HTML page
• JavaScript can react to events
• JavaScript can read and write HTML elements
• JavaScript can be used to validate input data
• JavaScript can be used to detect the visitor's
browser
• JavaScript can be used to create cookies
6

How and Where Do You
Place JavaScript Code?

How to put a JavaScript code into
an HTML page?
• Use the <script> tag (also use the type attribute to define the
scripting language)

<html>
<head>
<script type="text/javascript">
...
</script>
</head>
<body>
...
</script>
</body>
</html> 8

Where Do You Place Scripts?

• Scripts can be in the either <head> section or
<body> section
• Convention is to place it in the <head> section

<html>
<head>
....
</script>
</head>

9

Referencing External JavaScript
File
• Scripts can be provided locally or remotely
accessible JavaScript file using src attribute

<html>
<head>
<script language="JavaScript"
type="text/javascript"
src="http://somesite/myOwnJavaScript.js">
</script>
<script language="JavaScript"
type="text/javascript"
src="myOwnSubdirectory/myOwn2ndJavaScript.js">
</script>
10

JavaScript Variable

• You create a variable with or without the var
statement
var strname = some value
strname = some value
• When you declare a variable within a function, the
variable can only be accessed within that function
• If you declare a variable outside a function, all the
functions on your page can access it
• The lifetime of these variables starts when they are
declared, and ends when the page is closed
12

JavaScript Popup Boxes

• Alert box
> User will have to click "OK" to proceed
> alert("sometext")
• Confirm box
> User will have to click either "OK" or "Cancel" to proceed
> confirm("sometext")
• Prompt box
> User will have to click either "OK" or "Cancel" to proceed after
entering an input value
> prompt("sometext","defaultvalue")

13

JavaScript Language

• Conditional statement
> if, if.. else, switch
• Loop
> for loop, while loop
• try...catch
• throw

14

JavaScript Functions
(which behave like
Java methods)

More on Functions
in other Presentation

JavaScript Funcitons
• A JavaScript function contains some code that will
be executed only by an event or by a call to that
function
> To keep the browser from executing a script as soon as the
page is loaded, you can write your script as a function
• You may call a function from anywhere within the
page (or even from other pages if the function is
embedded in an external .js file).
• Functions can be defined either <head> or <body>
section
> As a convention, they are typically defined in the <head>
section 16

Example: JavaScript Function
<html>
<head>
// If alert("Hello world!!") below had not been written within a
// function, it would have been executed as soon as the page gets loaded.
function displaymessage() {
alert("Hello World!")
}
</script>
</head>
<body>
<form>
<input type="button" value="Click me!"
onclick="displaymessage()" >
</form>
</body>
</html>
17

Events & Event Handlers

• Every element on a web page has certain events
which can trigger invocation of event handlers
• Attributes are inserted into HTML tags to define
events and event handlers
• Examples of events
> A mouse click
> A web page or an image loading
> Mousing over a hot spot on the web page
> Selecting an input box in an HTML form
> Submitting an HTML form
> A keystroke 19

Events

• onabort - Loading of an image is interrupted
• onblur - An element loses focus
• onchange - The content of a field changes
• onclick - Mouse clicks an object
• ondblclick - Mouse double-clicks an object
• onerror - An error occurs when loading a document
or an image
• onfocus - An element gets focus
• onkeydown - A keyboard key is pressed
20

Events

• onkeypress - A keyboard key is pressed or held down
• onkeyup - A keyboard key is released
• onload - A page or an image is finished loading
• onmousedown - A mouse button is pressed
• onmousemove - The mouse is moved
• onmouseout - The mouse is moved off an element
• onmouseover - The mouse is moved over an element
• onmouseup - A mouse button is released
21

Events

• onreset - The reset button is clicked
• onresize - A window or frame is resized
• onselect - Text is selected
• onsubmit - The submit button is clicked
• onunload - The user exits the page

22

onload & onUnload Events

• The onload and onUnload events are triggered when
the user enters or leaves the page
• The onload event is often used to check the visitor's
browser type and browser version, and load the
proper version of the web page based on the
information
• Both the onload and onUnload events are also often
used to deal with cookies that should be set when a
user enters or leaves a page.

23

onFocus, onBlur and onChange

• The onFocus, onBlur and onChange events are
often used in combination with validation of form
fields.
• Example: The checkEmail() function will be called
whenever the user changes the content of the field:
<input type="text" size="30"
id="email" onchange="checkEmail()">;

24

Example & Demo: onblur
<html>
<head>
function upperCase() {
var x=document.getElementById("fname").value
document.getElementById("fname").value=x.toUpperCase()
}
</script>
</head>
<body>
Enter your name:
<input type="text" id="fname" onblur="upperCase()">
</body>
</html>

25

onSubmit

• The onSubmit event is used to validate all form
fields before submitting it.
• Example: The checkForm() function will be called
when the user clicks the submit button in the form. If
the field values are not accepted, the submit should
be canceled. The function checkForm() returns
either true or false. If it returns true the form will be
submitted, otherwise the submit will be cancelled:
<form method="post" action="xxx.html"
onsubmit="return checkForm()">

26

Example & Demo: onSubmit
<html>
<head>
function validate() {
// return true or false based on validation logic
}
</script>
</head>
<body>
<form action="tryjs_submitpage.htm" onsubmit="return validate()">
Name (max 10 chararcters): <input type="text" id="fname" size="20"><br />
Age (from 1 to 100): <input type="text" id="age" size="20"><br />
E-mail: <input type="text" id="email" size="20"><br />
<br />
<input type="submit" value="Submit">
</form>
</body>
</html>
27

onMouseOver and onMouseOut

• onMouseOver and onMouseOut are often used to
create "animated" buttons.
• Below is an example of an onMouseOver event. An
alert box appears when an onMouseOver event is
detected:
<a href="http://www.w3schools.com"
onmouseover="alert('An onMouseOver event');return false">
<img src="w3schools.gif" width="100" height="30">
</a>

28

JavaScript Object

• JavaScript is an Object Oriented Programming (OOP)
language
• A JavaScript object has properties and methods
> Example: String JavaScript object has length property and
toUpperCase() method
var txt="Hello World!"
document.write(txt.length)
document.write(txt.toUpperCase())
</script>
30

JavaScript Built-in Objects

• String
• Date
• Array
• Boolean
• Math

31

JavaScript Object vs. Java Object

• Simlarities
> Both has properties and methods
• Differences
> JavaScript object can be dynamically typed while Java object
is statically typed
> In JavaScript, properties and methods are dynamically added

32

JavaScript Objects;
3 Different Ways of
Creating JavaScript
Objects

Creating Your Own JavaScript Objects

• 3 different ways
> Create a direct instance of an object by using built-in
constructor for the Object class
> Create a template (Constructor) first and then create an
instance of an object from it
> Create object instance as Hash Literal

34

Option 1: Creating a Direct Instance
of a JavaScript Object
• By invoking the built-in constructor for the Object class
personObj=new Object(); // Initially empty with no properties or methods
• Add properties to it
personObj.firstname="John";
personObj.age=50;
• Add an anonymous function to the personObj
personObj.tellYourage=function(){
alert(“This age is ” + this.age);
}
// You can call then tellYourage function as following
personObj.tellYourage();
35

Option 1: Creating a Direct Instance
of a JavaScript Object
• Add a pre-defined function
function tellYourage(){
alert(“The age is” + this.age);
}
personObj.tellYourage=tellYourage;
• Note that the following two lines of code are doing
completely different things
// Set property with a function
personObj.tellYourage=tellYourage;
// Set property with returned value of the function
personObj.tellYourage=tellYourage();
36

Option 2: Creating a template of a
JavaScript Object
• The template defines the structure of a JavaScript
object in the form of a function
• You can think of the template as a constructor
function Person(firstname,lastname,age,eyecolor) {
this.firstname=firstname;
this.lastname=lastname;
this.age=age;
this.tellYourage=function(){
alert(“This age is ” + this.age);
}
}
37

Option 2: Creating a template of a
JavaScript Object
• Once you have the template, you can create new
instances of the object
myFather=new Person("John","Doe",50,"blue");
myMother=new Person("Sally","Rally",48,"green");
• You can add new properties and functions to new
objects
myFather.newField = “some data”;
myFather.myfunction = function() {
alert(this["fullName"] + ” is ” + this.age);
}

38

Option 3: Creating JavaScript
Object as a Hash Literal
• Create personObj JavaScript object
var personObj = {
firstname: "John",
lastname: "Doe",
age: 50,
tellYourage: function () {
alert(“The age is ” + this.age );
}
tellSomething: function(something) {
alert(something);
}
}

personObj.tellYourage();
personObj.tellSomething(“Life is good!”); 39

JavaScript Objects:
Hash (Associative Array)

JavaScript Object is an Associative
Array (Hash)
• A JavaScript object is essentially an associative array (hash)
with fields and methods, which are keyed by name
{
firstname: "John",
lastname: "Doe",
age: 50,
tellYourage: function () {
alert(“The age is ” + this.age );
},
tellSomething: function(something) {
alert(something);
}
}

• The following two lines of code are semantically
equivalent
myObject.myfield = “something”;
myObject['myfield'] = “something”;
41

JavaScript Objects:
Classes, Objects,
Inheritance

JavaScript has No built-in concept
of Inheritance
• JavaScript has a concept of objects and classes
(like in Java) but no built-in concept of inheritance
(unlike in Java)
> Every JavaScript object is really an instance of the same base
class, a class that is capable of binding member fields and
functions to itself at runtime

43

prototype

• A prototype is a property of every JavaScript object
• Functions and properties can be associated with a
constructor's property
• When a function is invoked with new keyword, all
properties and methods of the prototype for the
function are attached to the resulting object

45

prototype
// Constructor of the MyObject
function MyObject(name, size){
this.name=name;
this.size=size;
}
// Add a function to the prototype
MyObject.prototype.tellSize=function{
alert(“size of “ + this.name+” is “ + this.size);
}

// Create an instance of the object. The new object has tellSize() method.
var myObj=new MyObject(“Sang”, “30 inches”);
myObj.tellSize();

46

JavaScript Objects:
Functions Again

A function is a first-class
JavaScript Object
• Functions are a bit like Java methods
> They have arguments and return values
• A function is a first-class object in JavaScript (unlike
in Java)
> Can be considered as a descendant of Object
> Can do everything a regular JavaScript object can do such as
storing properties by name
> Function objects can have other function objects as methods

48

A function can take Variable
arguments
• You can call myfunction() or myfunction(20)

function myfunction(value){
if (value){
this.area=value;
}
return this.area;
}

49

HTML DOM

• The HTML DOM defines a standard set of objects
for HTML, and a standard way to access and
manipulate HTML documents
• All HTML elements, along with their containing text
and attributes, can be accessed through the DOM.
> The contents can be modified or deleted, and new elements
can be created.
• The HTML DOM is platform and language
independent
> It can be used by any programming language like Java,
JavaScript, and VBScript
52

HTML DOM Objects

• Anchor object
• Document object
• Event object
• Form and Form Input object
• Frame, Frameset, and IFrame objects
• Image object
• Location object
• Navigator object
53

HTML DOM Objects

• Option and Select objects
• Screen object
• Table, TableHeader, TableRow, TableData objects
• Window object

54

Document Object: Write text to the
output
<html>
<body>
document.write("Hello World!")
</script>
</body>
</html>

56

Document Object: Write text with
Formatting to the output
<html>
<body>
document.write("<h1>Hello World!</h1>")
</script>
</body>
</html>

57

Document Object: Use
getElementById()
<html>
<head>
function getElement() {
var x=document.getElementById("myHeader")
alert("I am a " + x.tagName + " element")
}
</script>
</head>
<body>
<h1 id="myHeader" onclick="getElement()">Click to see what element I am!</h1>
</body>
</html>

58

Document Object: Use
getElementsByName()
<html>
<head>
function getElements() {
var x=document.getElementsByName("myInput")
alert(x.length + " elements!")
}
</script>
</head>
<body>
<input name="myInput" type="text" size="20"><br />
<br />
<input type="button" onclick="getElements()" value="How many elements named
'myInput'?">
</body>
</html>
59

Document Object: Return the innerHTML
of the first anchor in a document
<html>
<body>
<a name="first">First anchor</a><br />
<a name="second">Second anchor</a><br />
<a name="third">Third anchor</a><br />
<br />
InnerHTML of the first anchor in this document:
document.write(document.anchors[0].innerHTML)
</script>
</body>
</html>

60

Document Object: Access an item in a
collection
<html>
<body>
<form id="Form1" name="Form1">
Your name: <input type="text">
</form>
<form id="Form2" name="Form2">
Your car: <input type="text">
</form>
<p>
To access an item in a collection you can either use the number or the name of the item:
</p>
document.write("<p>The first form's name is: " + document.forms[0].name + "</p>")
document.write("<p>The first form's name is: " + document.getElementById("Form1").name
+ "</p>")
</script>
</body> 61

Event Object: What are the
coordinates of the cursor?
<html>
<head>
function show_coords(event) {
x=event.clientX
y=event.clientY
alert("X coords: " + x + ", Y coords: " + y)
}
</script>
</head>
<body onmousedown="show_coords(event)">
<p>Click in the document. An alert box will alert the x and y coordinates of the
cursor.</p>
</body>
</html>

63

Event Object: What is the unicode
of the key pressed?
<html>
<head>
function whichButton(event) {
alert(event.keyCode)
}
</script>
</head>
<body onkeyup="whichButton(event)">
<p><b>Note:</b> Make sure the right frame has focus when trying this example!</p>
<p>Press a key on your keyboard. An alert box will alert the unicode of the key
pressed.</p>
</body>
</html>

64

Event Object: Which element was
clicked?
<html>
<head>
function whichElement(e) {
var targ
if (!e) var e = window.event
if (e.target) targ = e.target
else if (e.srcElement) targ = e.srcElement
if (targ.nodeType == 3) // defeat Safari bug
targ = targ.parentNode
var tname
tname=targ.tagName
alert("You clicked on a " + tname + " element.")
}
</script>
</head>
<body onmousedown="whichElement(event)">
<p>Click somewhere in the document. An alert box will alert the tag name of the element you clicked on.</p>
<h3>This is a header</h3>
<p>This is a paragraph</p>
<img border="0" src="ball16.gif" width="29" height="28" alt="Ball">
</body>
65

Event Object: Which event type
occurred?
<html>
<head>
function whichType(event) {
alert(event.type)
}
</script>
</head>
<body onmousedown="whichType(event)">
<p>
Click on the document. An alert box will alert which type of event occurred.
</p>
</body>
</html>
66

JavaScript Basics

Sang Shin
Java Technology Architect
Sun Microsystems, Inc.
sang.shin@sun.com
www.javapassion.com

JavaScript

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