JavaScript is a client side scripting language, first it is only used for validation purpose but now it is used to many things including postback, database connections, get response, call backs etc.
JavaScript is a programming language that adds interactivity to your website (for example: games, responses when buttons are pressed or data entered in forms, dynamic styling, animation). JavaScript is the programming language of HTML and the Web. Programming makes computers do what you want them to do.
JavaScript is easy to learn.
check out below links for more details
https://developer.mozilla.org/en-US/Learn/Getting_started_with_the_web/JavaScript_basics
http://www.w3schools.com/js/
Thanks
Koolprasd2003
Editor, DotNetSpider MVM
Microsoft MVP 2014 [ASP.NET/IIS]