index.js

const YEAR_IN_MS = 3.154e+10;
const MONTH_IN_MS = 2.628e+9;
const WEEK_IN_MS = 6.048e+8;
const DAY_IN_MS = 8.64e+7
const HOUR_IN_MS = 3.6e+6;
const MINUTE_IN_MS = 60000;
const SECOND_IN_MS = 1000;

let converterFactory = (millisecondUnit) => {
    return (value) => {
        return {
            get in() {
                return {
                    get years() {
                        return value * millisecondUnit / YEAR_IN_MS;
                    },
                    get months() {
                        return value * millisecondUnit / MONTH_IN_MS;
                    },
                    get weeks() {
                        return value * millisecondUnit / WEEK_IN_MS;
                    },
                    get days() {
                        return value * millisecondUnit / DAY_IN_MS;
                    },
                    get hours() {
                        return value * millisecondUnit / HOUR_IN_MS;
                    },
                    get minutes() {
                        return value * millisecondUnit / MINUTE_IN_MS;
                    },
                    get seconds() {
                        return value * millisecondUnit / SECOND_IN_MS;
                    },
                    get milliseconds() {
                        return value * millisecondUnit;
                    }
                };
            }
        };
    }
};

let yearConverter = (value) => {
    return {
        get in() {
            return {
                get years() {
                    return value;
                },
                get months() {
                    return value * 12;
                },
                get weeks() {
                    return value * 52;
                },
                get days() {
                    return value * 365;
                },
                get hours() {
                    return value * YEAR_IN_MS / HOUR_IN_MS;
                },
                get minutes() {
                    return value * YEAR_IN_MS / MINUTE_IN_MS;
                },
                get seconds() {
                    return value * YEAR_IN_MS / SECOND_IN_MS;
                },
                get milliseconds() {
                    return value * YEAR_IN_MS;
                }
            }
        }
    };
};

const monthConverter = converterFactory(MONTH_IN_MS);
const weekConverter = converterFactory(WEEK_IN_MS);
const dayConverter = converterFactory(DAY_IN_MS);
const hourConverter = converterFactory(HOUR_IN_MS);
const minuteConverter = converterFactory(MINUTE_IN_MS);
const secondConverter = converterFactory(SECOND_IN_MS);
const millisecondConverter = converterFactory(1.0);

let MrTime = (value) => {
    if(value === null || !isFinite(value)) {
        throw new Error(`Invalid time value given: ${value}`);
    }

    return {
        get years() {
            return yearConverter(value);
        },
        get months() {
            return yearConverter(value / 12);
        },
        get weeks() {
            return weekConverter(value);
        },
        get days() {
            return dayConverter(value);
        },
        get hours() {
            return hourConverter(value);
        },
        get minutes() {
            return minuteConverter(value);
        },
        get seconds() {
            return secondConverter(value);
        },
        get milliseconds() {
            return millisecondConverter(value)
        }
    };
};

module.exports = MrTime;