JavaScript DAY - 1
What is JavaScript?
Ø JavaScript (JS) is a lightweight, dynamic computer
programming languageand designed for creating
network-centric applications.
Ø It is most commonly used as a part of web pages, whose
implementations allow client-side script to interact with the user and make
dynamic pages.
Ø It is an interpreted programming language with
object-oriented capabilities.
Ø 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.
Ø It is open and cross-platform.
Immediately
Advantages of JavaScript
The merits of using
JavaScript are −
Ø 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.
Ø Immediate feedback to the visitors − They don't have to wait for a page
reload to see if they have forgotten to enter something.
Ø Increased interactivity − You can create interfaces that
react when the user hovers over them with a mouse or activates them via the
keyboard.
Ø 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 −
Ø Client-side JavaScript does not allow the reading or
writing of files. This has been kept for security reason.
Ø JavaScript cannot be used for networking applications
because there is no such support available.
Ø JavaScript doesn't have any multithreading or
multiprocessor capabilities.
JavaScript Development Tools
Ø Text editor such as Notepad.
Ø Any web browser as a compiler.
JavaScript Script Syntax
Ø
JavaScript can be
implemented using JavaScript statements that are placed within the <script>...
</script> HTML tags in a web page.
Ø
Normally<script> tags should keep within the <head> tags.
Ø
The <script> tag
alerts the browser program to start interpreting all the text between these
tags as a script.
Ø The
script tag takes two important attributes −
1.
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.
2.
Type − This attribute is what is now
recommended to indicate the scripting language in use and its value should be
set to "text/javascript".
<html>
<body>
<scriptlanguage="javascript"type="text/javascript">
<!--
document.write("Hello World!");
//
- ->
</script>
</body>
</html>
Ø JavaScript is case sensitive. Keywords are lowercase but variables
can be mixed of lower and uppercase characters like myVal.
Ø // is used for single line comment and /* */ are used for multiline comments.JavaScript also recognizes the HTML comment opening sequence
<!- - and the closing sequence should be written as //-->.
Ø Semicolons are used to terminate the statements but are optional. It is a good programming practice to use
semicolons.
Ø JavaScript ignores spaces, tabs, and newlines that
appear in JavaScript programs.
Ø The
function document.write which writes a string into our HTML
document. This function can be used to write text, HTML, or both.
Practical
Write a JavaScript code to display the text “Welcome to Home” and
run it.
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