History and Versions JavaScript

JavaScript has one specification and several dialects:

ECMAScript - The official name of the JavaScript language specification, the ECMA-262 specification.
    JavaScript - The originating dialect of the ECMAScript language specification. JavaScript was implemented in Netscape.
    LiveScript - The predecessor of JavaScript. LiveScript was renamed to JavaScript in Netscape 3.0.
    JScript - The Microsoft dialect of the ECMAScript language specification. JScript was first implemented in Internet Explorer 3.0 browser released in August 1996.
    JScript .NET - The successor of JScript under Microsoft's .NET framework.

Here is a quick summary of JavaScript history and versions of its dialects:

1994   Netscape 1.0
199?   Netscape 2.0/JavaScript 1.0   ECMA-262 Edition 1, 1997
1996   IE 3.0/JScript 1.0            ECMA-262 Edition 1, 1997
199?   Netscape 3.0/JavaScript 1.1   ECMA-262 Edition 1, 1997
1997   IE 4.0/JScript 3.0            ECMA-262 Edition 1, 1997
199?   Netscape 4.0/JavaScript 1.2   ECMA-262 Edition 1, 1997
1999   IE 5.0/JScript 5.0            ECMA-262 Edition 1, 1997
2000   Netscape 6.0/JavaScript 1.5   ECMA-262 Edition 3, 1999
2000   IE 5.5/JScript 5.5            ECMA-262 Edition 3, 1999
2001   IE 6.0/JScript 5.6            ECMA-262 Edition 3, 1999
2002   Netscape 7.0/JavaScript 1.5   ECMA-262 Edition 3, 1999
2004   Firefox 1.0                   ECMA-262 Edition 3, 1999
2006   IE 7.0/JScript ?              ECMA-262 Edition 3, 1999
2006   Firefox 2.0/JavaScript 1.7    ECMA-262 Edition 3, 1999
2007   Netscape 8.0/JavaScript ?     ECMA-262 Edition ?
2008   IE 8.0/JScript ?              ECMA-262 Edition ?
200?   Firefox 3.0/JavaScript 1.8    ECMA-262 Edition ?
2011   Firefox 4.0/JavaScript 1.8.5  ECMA-262 Edition ?

The latest version of JavaScript specification is ECMA-262 Edition 3. So we should use it as the main reference to learn JavaScript.