JavaScript Introduction

ABOUT

Created by Netscape in 1995 as an extension of HTML for Netscape Navigator 2.0, JavaScript had as its main function the manipulation of HTML documents and form validation. Before winning this name so famous nowadays, JavaScript was called Mocha. When it first shipped in beta releases, it was officially called LiveScript and finally, when it was released by Sun Microsystems, was baptized with the name by which it is known today. Because of the similar names, people confuse JavaScript with Java. Although both have the lexical structure of programming, they are not the same language. Different from C, C# and Java, JavaScript is an interpreted language. It means that it needs an "interpreter". In case of JavaScript, the interpreter is the browser.
CURRENT VERSION

The JavaScript standard is ECMAScript. As of 2012, all modern browsers fully support ECMAScript 5.1. Older browsers support at least ECMAScript 3. As of June 2015 the spec for ES6/ES2015 has been approved. See the ECMAScript 2015 Language Specification at Ecma International.

A good reference to versions, references and news about JavaScript can be found at the Mozilla Developer Network.
THE DOM

The Document Object Model (DOM) is an API for HTML and XML documents. It provides a structural representation of the document, enabling you to modify its content and visual presentation by using a scripting language such as JavaScript. See more at Mozilla Developer Network - DOM.
 

source: http://jstherightway.org/#getting-started