1.0.0 • Public • Published

    Typed Date Converter

    Well, what is it?

    It is an attempt to create an approach for converting primitive dates (numbers/strings) into object types (Date, Moment, etc.) for typescript, without the need to describe them in a separate interface.

    For example, you get from api:

    interface User {
      registered: string;
      name: string;
      lastLoginDate: string | null;
      details: Details;
      activities: Activity[];
    interface Details {
      birthday: string;
      place: string;
    interface Activity {
      place: string;
      date: string;

    but in the application you need the convert the User.registered, User.lastLoginDate, Details.birthday and Activity.date to Date. What now? Create a new interface for each of these with this type, or modify existing one for using generic? This is the problem this package tries to tackle: convert all dates from one type to another and return a new typed entity without the need to manually create new interfaces.

    Well, how to use it?

    Install with

    npm i @merry-solutions/typed-date-converter

    Next, the interface used for converting should be turned into a 'super' interface, to include all possible date types, this is required for proper converted result typings. So let's add Date type to the union of fields we intend to convert:

    interface User {
      registered: string | Date;
      name: string;
      lastLoginDate: string | Date | null;
      details: Details;
      activities: Activity[];
    interface Details {
      birthday: string | Date;
      place: string;
    interface Activity {
      place: string;
      date: string | Date;

    This is required for proper typing of the output. Now we need some functions for checking and converting the fields:

    • to check if the property is primitive fit for conversion to object date;
    • to check if object is date which requires conversion into primitive;
    • to convert primitive to a date object;
    • to convert date object to a primitive.

    For the sake of simplicity, let's assume our dates come always in format YYYY-MM-DD. So our functions would look the following way:

    import {
    } from '@merry-solutions/typed-date-converter';
    const converterToJsDate: StringToJSDateConverter<string, Date> = (d: string) => new Date(d);
    const converterFromJsDate:JSDateToStringConverter<Date, string> = (d: Date) => d.toISOString();
    const checkTypeofDate: CheckTypeofObjectDate = (v: unknown) => v instanceof Date;
    // if string is YYYY-MM-DD, we assume it is a date string
    const checkTypeofPrimitive: CheckTypeofPrimitiveDate = (v: string | number) => typeof v === 'string' && /^\d{4}(-\d{2}){2}$/.test(v);
    const deepDateConverter = createRecursiveDateConverter<string, Date>({

    There, we have a converter ready for usage. Now assuming we have a user

    const user: User = {
      registered: '1970-12-12',
      name: 'Bob',
      lastLoginDate: null,
      details: {
        birthday: '1970-12-12',
        place: 'some village',
      activities: [
          date: '1970-12-12',
          place: 'not specified',

    our conversion would go as following:

    const convertedUser = deepDateConverter<User, Date>(user);
    // now all these fields are Date: mappedUser.registered, mappedUser.details.birthday, mappedUser.activities[0].date

    To convert back to string dates we could do the same process to the object we received, passing different types:

    const converteToPrimitiveDatesdUser = deepDateConverter<typeof convertedUser, string>(convertedUser);
    // now all these fields are back to string: mappedUser.registered, mappedUser.details.birthday, mappedUser.activities[0].date

    Don't forget to pass types to the converter, so the IDE knows the correct type.

    Simple as that :)


    npm i @merry-solutions/typed-date-converter

    DownloadsWeekly Downloads






    Unpacked Size

    9.28 kB

    Total Files


    Last publish


    • bwca