how many microseconds fit in a safe JS integer?

microseconds-stuff.js

'use strict'

const max = Number.MAX_SAFE_INTEGER // 9007199254740991

console.log('Number.MAX_SAFE_INTEGER:  ', nice(max))
console.log('')

// Number.MAX_SAFE_INTEGER:   9,007,199,254,740,991

console.log('how many time units fit in', nice(max), 'microseconds')

const unitScs = max / 1000 / 1000
const unitMns = unitScs / 60
const unitHrs = unitMns / 60
const unitDys = unitHrs / 24
const unitYrs = unitDys / 365

// how many seconds fit in MAX_SAFE_INTEGER?
console.log('  seconds:', nice(unitScs))
console.log('  minutes:', nice(unitMns))
console.log('  hours:  ', nice(unitHrs))
console.log('  days:   ', nice(unitDys))
console.log('  years:  ', nice(unitYrs))

// how many time units fit in 9,007,199,254,740,991 microseconds
//   seconds:         9,007,199,255
//   minutes:           150,119,988
//   hours:               2,502,000
//   days:                  104,250
//   years:                     286

// double check the years value
const check = unitYrs * 365 * 24 * 60 * 60 * 1000 * 1000
console.log('')
console.log('double checking the years value:')
console.log('  years as microseconds:         ', nice(check))
console.log('  Number.MAX_SAFE_INTEGER - that:', nice(max - check))

// double checking the years value:
//   years as microseconds:          9,007,199,254,740,990
//   Number.MAX_SAFE_INTEGER - that:                     1

function nice(n) {
  return right(commaize(ceil(n)), 21)
}

function right(s, len, pad) {
  pad = pad || ' '
  s = '' + s
  while (s.length < len) s = pad + s
  return s
}

function commaize(n) {
  n = '' + n
  n = reverse(n)

  let result = []
  while (n.length > 0) {
    result.push(reverse(n.substr(0, 3)))
    n = n.substr(3)
  }

  return result.reverse().join(',')
}

function ceil(n) { return Math.ceil(n) }
function reverse(s) { return s.split('').reverse().join('')}