How to check which version of v8 is installed with my NodeJS?

Just run npm version (don't know since when this is available)

> npm version
{ http_parser: '1.0',
  node: '0.10.35',
  v8: '3.14.5.9',
  ares: '1.9.0-DEV',
  uv: '0.10.30',
  zlib: '1.2.8',
  modules: '11',
  openssl: '1.0.1j',
  npm: '1.4.28',
  xsjs: '0.1.5' }

Easy way:
Type in command line: node -p process.versions.v8

Hard way:

1. Type node --version to get the Node.js version.

2. Go to the Node.js Changelogs.

3. Find and open an appropriate Node.js version change log.

4. Look for notes containing V8 to.

One-line solution:
node -p process.versions.v8

Alternative solution:
node -e "console.log(process.versions.v8)"