save.js

function save({
  initialInvestment = 0,
  baseMonthly,
  contributionChangePercentageYearly,
  contributionChangeFn,
  returnPercentageYearly,
  durationYears,
  accumulatedExpense = 0,
  accumulatedValue = 0,
  values = [],
  originalValues
}) {
  if (!durationYears--) {
    const formattedValues = values.map(row => {
      return Object.keys(row).reduce((acc, column) => {
        var cell = row[column]
        return {
          ...acc,
          [column]: typeof cell === 'number' ? cell.toLocaleString() : cell
        }
      }, {})
    })
    console.clear()
    console.table(JSON.parse(JSON.stringify(originalValues)))
    console.table(formattedValues)
    return accumulatedValue
  }
  const newBaseMonthly = (
    baseMonthly + (
      contributionChangeFn
        ? contributionChangeFn(baseMonthly, (originalValues?.durationYears ?? 0) - durationYears)
        : baseMonthly * contributionChangePercentageYearly/100
    )
  )
  const newAccumulatedExpense = initialInvestment + accumulatedExpense + baseMonthly * 12
  const baseAccumulatedValue = initialInvestment + accumulatedValue + baseMonthly * 12
  const newAccumulatedValue = baseAccumulatedValue + baseAccumulatedValue * returnPercentageYearly/100
  return save({
    initialInvestment: 0,
    baseMonthly: newBaseMonthly,
    contributionChangePercentageYearly,
    contributionChangeFn,
    returnPercentageYearly,
    durationYears,
    accumulatedExpense: newAccumulatedExpense,
    accumulatedValue: newAccumulatedValue,
    values: values.concat({
      'monthly invest': baseMonthly,
      'accumulated expense': newAccumulatedExpense,
      'accumulated value': newAccumulatedValue
    }),
    originalValues: originalValues || {
      initialInvestment,
      baseMonthly,
      contributionChangePercentageYearly,
      contributionChangeFn: contributionChangeFn.toString().replace(/^.+\{/, '').replace(/\n/g, '').replace(/\s+\}$/, '').replace(/^\s+/, ''),
      returnPercentageYearly,
      durationYears: durationYears + 1
    }
  })
}


save({
  initialInvestment: 1000,
  baseMonthly: 100,
  contributionChangePercentageYearly: 5,
  returnPercentageYearly: 5,
  durationYears: 10
})

// or

save({
  baseMonthly: 100,
  contributionChangeFn(monthly, year) {
    return year < 5 ? monthly * 33/100 : 0
  },
  returnPercentageYearly: 5,
  durationYears: 10
})