How to measure memory usage in real time

memory-usage.js

const pidusage = require('pidusage')
const secTimeout = process.argv[2] ? parseInt(process.argv[2]): 3
const pid = parseInt(process.argv[3] || process.pid)

console.log('PID:', process.pid)
console.log('Monitoring of PID:', pid)
console.log('Time interval:', secTimeout, 'seconds')

const compute = async () => await pidusage(pid)
const wait = ms => new Promise(resolve => setTimeout(() => resolve(), ms))
const mb = (n = 0) => `${Math.floor(n / (1024 * 1024))}MB`
const percent = (n = 0, all = 1) => `${(100 * n / all).toFixed(1)}%`

const gen = async function *() {
  const stat = await compute()
  const startMemory = stat.memory
  const hrstart = process.hrtime()

  while(true) {
    const stat = await compute()
    const m = stat.memory

    const memStr = `mem - ${mb(m)}`

    yield memStr

    const diff = m - startMemory

    let memDiffStr = (diff >= 0) ? `: +${mb(diff)} (+${percent(diff, m)})` : `: ${mb(diff)} (${percent(diff, m)})`

    const memStrLen = memStr.length
    const memStrDiffLen = memDiffStr.length

    const cpuStr = `${stat.cpu.toFixed(1)}`
    const cpuStrLen = cpuStr.length

    yield memDiffStr
    yield ' '.repeat(40 - memStrLen - memStrDiffLen)
    yield '| '
    yield 'cpu - '
    yield cpuStr
    yield ' '.repeat(10 - cpuStrLen)
    yield '| '

    const hrend = process.hrtime(hrstart)

    const hours = Math.floor(hrend[0]/3600)
    const minutes = Math.floor(hrend[0]/60)%60
    const seconds = hrend[0]%60
    const milliseconds = (hrend[1] / 1000000).toFixed(3)

    const timeSpendStr = `${hours}h ${minutes}m ${seconds}s ${milliseconds}ms`
    yield timeSpendStr

    yield ' '.repeat(20 - timeSpendStr.length)
    yield '| '

    const dateStr = new Date().toString()
    yield dateStr

    yield ' '.repeat(60 - dateStr.length)
    yield '| '

    yield `\n`

    await wait(secTimeout * 1000)
  }
}

;(async () => {
  const run = gen()

  while(true) {
    const data = await run.next()
    process.stdout.write(data.value)
  }
})()