get CPU usage percent for a process in node, using proposed `process.cpuUsage()` function

cpu-percent.js

'use strict'

// see: https://github.com/nodejs/node/pull/6157

var startTime  = process.hrtime()
var startUsage = process.cpuUsage()

// spin the CPU for 500 milliseconds
var now = Date.now()
while (Date.now() - now < 500)

var elapTime = process.hrtime(startTime)
var elapUsage = process.cpuUsage(startUsage)

var elapTimeMS = secNSec2ms(elapTime)
var elapUserMS = secNSec2ms(elapUsage.user)
var elapSystMS = secNSec2ms(elapUsage.system)
var cpuPercent = Math.round(100 * (elapUserMS + elapSystMS) / elapTimeMS)

console.log('elapsed time ms:  ', elapTimeMS)
console.log('elapsed user ms:  ', elapUserMS)
console.log('elapsed system ms:', elapSystMS)
console.log('cpu percent:      ', cpuPercent)

function secNSec2ms (secNSec) {
  return secNSec[0] * 1000 + secNSec[1] / 1000000
}

The workable codes for node v12.x:

var startTime  = process.hrtime()
var startUsage = process.cpuUsage()

// spin the CPU for 500 milliseconds
var now = Date.now()
while (Date.now() - now < 500)

var elapTime = process.hrtime(startTime)
var elapUsage = process.cpuUsage(startUsage)

var elapTimeMS = secNSec2ms(elapTime)
var elapUserMS = secNSec2ms(elapUsage.user)
var elapSystMS = secNSec2ms(elapUsage.system)
var cpuPercent = Math.round(100 * (elapUserMS + elapSystMS) / elapTimeMS)

console.log('elapsed time ms:  ', elapTimeMS)
console.log('elapsed user ms:  ', elapUserMS)
console.log('elapsed system ms:', elapSystMS)
console.log('cpu percent:      ', cpuPercent)

function secNSec2ms (secNSec) {
  if (Array.isArray(secNSec)) { 
    return secNSec[0] * 1000 + secNSec[1] / 1000000; 
  }
  return secNSec / 1000; 
}

Thank you @aprilandjan