ix
Checking for Plug-Ins ................................................................................................................................... 366
Controlling Multimedia ............................................................................................................................... 367
33.
JAVASCRIPT – Debugging ...................................................................................................................... 369
Error Messages in IE .................................................................................................................................... 369
Error Messages in Firefox or Mozilla ........................................................................................................... 370
Error Notifications ....................................................................................................................................... 371
How to Debug a Script ................................................................................................................................. 371
Useful Tips for Developers .......................................................................................................................... 372
34.
JAVASCRIPT – Image Map ..................................................................................................................... 374
35.
JAVASCRIPT – Browsers ........................................................................................................................ 377
Navigator Properties ................................................................................................................................... 377
Navigator Methods ...................................................................................................................................... 378
Browser Detection ....................................................................................................................................... 379
11
What is JavaScript?
Javascript is a dynamic computer programming language. It is lightweight and most
commonly used as a part of web pages, whose implementations allow client-side
script to interact with the user and make dynamic pages. It is an interpreted
programming language with object-oriented capabilities.
JavaScript was first known as LiveScript , but Netscape changed its name to
JavaScript, possibly because of the excitement being generated by Java. JavaScript
made its first appearance in Netscape 2.0 in 1995 with the name LiveScript . The
general-purpose core of the language has been embedded in Netscape, Internet
Explorer, and other web browsers.
The
ECMA-262 Specification
defined a standard version of the core JavaScript
language.
JavaScript is a lightweight, interpreted programming language.
Designed for creating network-centric applications.
Complementary to and integrated with Java.
Complementary to and integrated with HTML.
Open and cross-platform.
Client-Side JavaScript
Client-side JavaScript is the most common form of the language. The script should
be included in or referenced by an HTML document for the code to be interpreted by
the browser.
It means that a web page need not be a static HTML, but can include programs that
interact with the user, control the browser, and dynamically create HTML content.
The JavaScript client-side mechanism provides many advantages over traditional CGI
server-side scripts. For example, you might use JavaScript to check if the user has
entered a valid e-mail address in a form field.
1.
JAVASCRIPT – OVERVIEW
12
The JavaScript code is executed when the user submits the form, and only if all the
entries
are valid , they would be submitted to the Web Server.
JavaScript can be used to trap user-initiated events such as button clicks, link
navigation, and other actions that the user initiates explicitly or implicitly.
Advantages of JavaScript
The merits of using JavaScript are:
Less server interaction: You can validate user input before sending the page
off to the server. This saves server traffic, which means less load on your
server.
Immediate feedback to the visitors: They don't have to wait for a page
reload to see if they have forgotten to enter something.
Increased interactivity: You can create interfaces that react when the user
hovers over them with a mouse or activates them via the keyboard.
Richer interfaces: You can use JavaScript to include such items as drag-and-
drop components and sliders to give a Rich Interface to your site visitors.
Limitations of JavaScript
We cannot treat JavaScript as a full-fledged programming language. It lacks the
following important features:
Client-side JavaScript does not allow the reading or writing of files. This has
been kept for security reason.
JavaScript cannot be used for networking applications because there is no such
support available.
JavaScript doesn't have any multithreading or multiprocessor capabilities.
Once again, JavaScript is a lightweight, interpreted programming language that
allows you to build interactivity into otherwise static HTML pages.
JavaScript Development Tools
One of major strengths of JavaScript is that it does not require expensive
development tools. You can start with a simple text editor such as Notepad. Since it
13
is an interpreted language inside the context of a web browser , you don't even need
to buy a compiler.
To make our life simpler, various vendors have come up with very nice JavaScript
editing tools. Some of them are listed here:
Microsoft FrontPage: Microsoft has developed a popular HTML editor called
FrontPage. FrontPage also provides web developers with a number of
JavaScript tools to assist in the creation of interactive websites.
Macromedia Dreamweaver MX: Macromedia Dreamweaver MX is a very
popular HTML and JavaScript editor in the professional web development
crowd. It provides several handy prebuilt JavaScript components, integrates
well with databases, and conforms to new standards such as XHTML and XML.
Macromedia HomeSite 5: HomeSite 5 is a well-liked HTML and JavaScript
editor from Macromedia that can be used to manage personal websites
effectively.
Where is JavaScript Today?
The ECMAScript Edition 5 standard will be the first update to be released in over four
years. JavaScript 2.0 conforms to Edition 5 of the ECMAScript standard, and the
difference between the two is extremely minor.
The specification for JavaScript 2.0 can be found on the following site:
http://www.ecmascript.org/
Today, Netscape's JavaScript and Microsoft's JScript conform to the ECMAScript
standard, although both the languages still support the features that are not a part
of the standard.
14
JavaScript can be implemented using JavaScript statements that are placed within
the
HTML tags in a web page.
You can place the tags, containing your JavaScript, anywhere within you
web page, but it is normally recommended that you should keep it within the
tags.
The
The script tag takes two important attributes:
Language: This attribute specifies what scripting language you are using.
Typically, its value will be javascript. Although recent versions of HTML (and
XHTML, its successor) have phased out the use of this attribute.
Type: This attribute is what is now recommended to indicate the scripting
language in use and its value should be set to "text/javascript".
So your JavaScript syntax will look as follows.
Your First JavaScript Code
Let us take a sample example to print out "Hello World". We added an optional HTML
comment that surrounds our JavaScript code. This is to save our code from a browser
that does not support JavaScript. The comment ends with a "//-->". Here "//"
signifies a comment in JavaScript, so we add that to prevent a browser from reading
2.
JAVASCRIPT – SYNTAX
15
the end of the HTML comment as a piece of JavaScript code. Next, we call a
function
document.write which writes a string into our HTML document.
This function can be used to write text, HTML, or both. Take a look at the following
code.
Sorry...JavaScript is needed to go ahead.
... ...
Click here for the result
4.
JAVASCRIPT – PLACEMENT
22
... portion of the document. In this case,
you would not have any function defined using JavaScript. Take a look at the following
code.
This is web page body
and
Sections
You can put your JavaScript code in
and section altogether as
follows.
.......
Set the variables to different values and then try...
Set the variables to different values and different operators and then
try...
38
Set the variables to different values and different operators and then
try...
Set the variables to different values and different operators and then
try...
Set the variables to different values and different operators and then
try...
Set the variables to different values and different operators and then
try...
Set the variables to different values and different operators and then
try...