Effective user age verification without handling photographs, credit card numbers, government ID etc.

verify.js

import timersPromises from 'node:timers/promises'

const FEB = 1
const MAR = 2

// `setTimeout` disallows numbers which don't fit into a signed 32-bit integer.
// In other words
const MAX_DELAY = 2 ** 31 - 1

const add18Years = date => {
  date = new Date(date)

  // Use local time.
  // If it's 29 February, skip forward to midnight on 1 March before adding 18 years
  if (
    date.getMonth() === FEB &&
    date.getDate() === 29
  ) {
    date.setMonth(MAR)
    date.setDate(1)
    date.setHours(0)
    date.setMinutes(0)
    date.setSeconds(0)
    date.setMilliseconds(0)
  }

  date.setFullYear(date.getFullYear() + 18)
  return date
}

const waitUntil = async date => {
  let remaining
  while ((remaining = date.getTime() - Date.now()) > MAX_DELAY) {
    await timersPromises.setTimeout(MAX_DELAY)
  }
  await timersPromises.setTimeout(remaining)
}

export const verifyAge = async () => {
  await waitUntil(add18Years(new Date()))
  return true
}

Usage:

import { verifyAge } from './verify.js'
const userIsOver18 = await verifyAge()