window.performance.now() equivalent in nodejs?

Node v8.5.0 has added Performance Timing API, which includes the performance#now(), e.g.

const {
  performance
} = require('perf_hooks');

console.log('performance', performance.now());

I would only mention that three of the reasons the author gives for the preference of the timing API in the browser wouldn't seem to apply directly to a node situation, and the fourth, the inaccuracy of Javscript time, cites an article from 2008, and I would strongly caution against relying on older material regarding Javascript performance specifics, particularly given the recent round of performance improvements all the engines have made to support "HTML5" apps.

However, in answer to your question, you should look at process.hrtime()

UPDATE: The present package (available via npm install present) provides some sugar around hrtime if you'd like it.

Note: Since the version 8.5.0 of Node, you can use performance.now()