Javascript overview and introduction to js

1. JavaScript Overview
What is JavaScript ?
 JavaScript started life as LiveScript, but Netscape changed the
name, possibly because of the excitement being generated by
Java.to JavaScript. JavaScript made its first appearance in
Netscape 2.0 in 1995 with a name LiveScript.
 JavaScript is a lightweight, interpreted programming language
with object-oriented capabilities that allows you to build
interactivity into otherwise static HTML pages.
 The general-purpose core of the language has been embedded
in Netscape, Internet Explorer, and other web browsers

JavaScript is:
 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 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 no longer be static HTML, but
can include programs that interact with the user, control the
browser, and dynamically create HTML content.
 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
explicitly or implicitly initiates.
Client-side JavaScript:

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 with JavaScript:
 We can not 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 can not be used for Networking applications because
there is no such support available.
 JavaScript doesn't have any multithreading or multiprocess
capabilities.

JavaScript Development Tools:
 One of JavaScript's strengths is that expensive development
tools are not usually required. You can start with a simple text
editor such as Notepad.
 Since it 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. Few of them are listed here:
– Microsoft FrontPage
– Macromedia Dreamweaver MX
– Macromedia HomeSite 5
– Yaldex Software Inc., Free JavaScript Editor

2. JavaScript Syntax
 A JavaScript consists of JavaScript statements that are placed within
the <script>... </script> HTML tags in a web page.
 You can place the <script> tag containing your JavaScript anywhere
within you web page but it is preferred way to keep it within the
<head> tags.
 The <script> tag alert the browser program to begin interpreting all
the text between these tags as a script. So simple syntax of your
JavaScript will be as follows (next slide)

Your First JavaScript Script:
<html>
<body>
<script language="javascript"
type="text/javascript">

</script>
</body>
</html>

 JavaScript ignores spaces, tabs, and newlines that appear in
JavaScript programs.
 Because you can use spaces, tabs, and newlines freely in your
program so you are free to format and indent your programs in
a neat and consistent way that makes the code easy to read
and understand.
Semicolons are Optional:
 Simple statements in JavaScript are generally followed by a
semicolon character, just as they are in C, C++, and Java.
JavaScript, however, allows you to omit this semicolon if your
statements are each placed on a separate line. For example, the
following code could be written without semicolons
Whitespace and Line Breaks:

• JavaScript is a case-sensitive language. This means that
language keywords, variables, function names, and any other
identifiers must always be typed with a consistent capitalization
of letters.
• So identifiers Time, TIme and TIME will have different meanings
in JavaScript.
• NOTE: Care should be taken while writing your variable and
function names in JavaScript.
Case Sensitivity:

Comments in JavaScript:
• JavaScript supports both C-style and C++-style comments, Thus:
• Any text between a // and the end of a line is treated as a
comment and is ignored by JavaScript.
• Any text between the characters /* and */ is treated as a
comment. This may span multiple lines.
• JavaScript also recognizes the HTML comment opening
sequence  is not recognized by
JavaScript so it should be written as //-->.

Example 1:
<script language="javascript" type="text/javascript">

</script>

Example 2:
<html>
<head>
<script>
function displayDate()
{
document.getElementById("demo").innerHTML=Date();
}
</script>
</head>
<body>
<h1>My First JavaScript</h1>
<p id="demo">This is a paragraph.</p>
<button type="button" onclick="displayDate()">Display
Date</button>
</body>
</html>

Javascript overview and introduction to js

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