Version 1: ECMAScript in 1997
Version 2: ECMAScript 2 in 1998 & Version 3: ECMAScript 3 in 1999
Version 4: Never released
Version 5: ECMAScript 5 in 2009
After version 3, ECMAScript 3.1 was renamed as ECMAScript 5 and released in 2009. This version had only a few changes.
Version 6: ECMAScript 2016