Pretty print money amounts

amount.js

exports.amount = function(amount) {
    if (isNaN(amount)) return exports.amount(0)
    if (amount < 0) return `-${exports.amount(-amount)}`

    let result = (Math.round(amount * 100) + '').padStart(3, '0')
    let [number, float] = [result.slice(0, -2), result.slice(-2)]
    let thousands = []

    for (let i = 1; -3 * i >= -number.length; i++) {
        thousands.unshift(number.slice(-3 * i, (-3 * i + 3) || undefined))
    }

    let residue = number.length % 3
    if (residue > 0) thousands.unshift(number.slice(0, residue))

    return `${thousands.join('.')},${float} €`
}