how to know which javascript version in my NODEJS?

I want to know which javascript version is my NodeJS is supporting ?

Use process.versions. From that page in the documentation:

console.log(process.versions);

outputs

{ node: '0.4.12',
  v8: '3.1.8.26',
  ares: '1.7.4',
  ev: '4.4',
  openssl: '1.0.0e-fips' }

EDIT: V8 uses the ECMAScript as specified in ECMA-262, 5th edition.

Reference: http://code.google.com/p/v8/