JavaScript
What is JAVASCRIPT JavaScript is a prototype-based script language which is based on Object Oriented
Programming concept. Its syntax is quite similar to c, c++ and Java. Web designers use JavaScript to add
certain kind of interactivity to web pages. It's not possible to make interactive web pages using only
HTML. By using HTML tags web browsers are being able to display just a structure and the layout of a
web page document on a window. So, using JavaScript together with HTML web designers creating
interactive web pages that can understand and process user behavior (actions) and respond them.
History and Evolution JavaScript originally called as Mocha, later LiveScript and Finally JavaScript. A
computer programmer named Brenden Eich was the creator of JavaScript. In the beginning JavaScript
was only used for the Netscape Navigator web browser under the Netscape Communications
Corporations.
- In September 1995 when the time Netscape Navigator Browser 2.0 Beta releases JavaScript was still
called "LiveScript".
- But in December 1995 when the time Netscape Navigator Browser version 2.0B3 released with Sun
Microsystems LiveScript was renamed as JavaScript. It was the JavaScript 1.0 version.
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In August 1996 Microsoft released Internet Explorer 3.0 with JavaScript 1.0 version.
Based on JavaScript they released JScript 1.0 version for Internet explorer 3.0 version. They named it
as JScript to avoid the license and trademark issues with Netscape.
Netscape navigator 3.0 was released with JavaScript 1.1 version.
In November Netscape submitted the JavaScript to Ecma International and as a result of that they
released ECMAScript language.
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In 1997 Netscape Navigator 4.0 was released with JavaScript 1.2 version.
Microsoft Internet Explorer 4.0 was released with Jscript 3.0 version similar with JavaScript 1.2
version.
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In 1998 Netscape Navigator 4.5 was released with JavaScript 1.3 version.
- In March 1999 Microsoft Internet Explorer 5.0 was released with JScript 5.0 similar with JavaScript
1.4 version.
- In November 2000 Netscape Navigator 6.0, Mozilla Firefox 1.0, Opera 6.0, Safari 3.0-5, Google
chrome 1.0-10.0 was released with JavaScript 1.5 version.
Microsoft Internet Explorer 5.5 was released with Jsript 5.5 version similar to JavaScript 1.5 version.
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In November 2005 Mozilla Firefox 1.5 was released with JavaScript 1.6 version.
- In October 2006 Mozilla Firefox 2.0 and Opera 11.50 versions was released with JavaScript 1.7
version.
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In June 2008 Mozilla Firefox 3.0 was released with JavaScript 1.8 version.
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In 2009 Mozilla Firefox 3.5 was released with JavaScript 1.8.1 version.
In June 2009 Mozilla Firefox 3.6 was released with JavaScript 1.8.2 version.
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In July 2010 Mozilla Firefox 4 and Internet Explorer 9 was released with JavaScript 1.8.5 version.
Browser compatibility -
Advantages and Disadvantages Advantages 
Validate the forms at the client-side saving both the precious server resources and time.

Change page contents dynamically.

Make online games.

Help to add interactivity to web pages.
Ex: Create mouseover effects, Change background color of document with a click of a button.

Randomly display content without the involvement of server programs.

Load content in new browser window and frames.
Disadvantages 
Reduces search engine friendliness.

JavaScript codes are need to store in separate java script source files. If not it'll cause to
expand the web pages you design.

JavaScript doesn't support for every browser.

Different browsers read JavaScript programs differently.
ReferencesWikipedia
Javascripter
Javasamples