TypeScript icon, indicating that this package has built-in type declarations

    0.0.8 • Public • Published

    ts-cast · Coverage Status npm version npm downloads GitHub license

    Runtime type checking for Typescript and JavaScript projects. It allows to specify data structures of the "external" resources (requests to the application or responses from other applications).

    The idea is based on the Caster that is a function accepts value of unknown type and returns value of target type or throws a TypeError if casting is impossible.

    Additionally ts-cast presents tools for:

    • validation casted data
    • transformation of casted data
    • Either and Validation monads support

    Almost in all cases ts-cast allows to avoid specification of correspondent type in TypeScript, because the type could be get as ReturnType of the correspondent caster-function.

    const Person = struct({ name: string, age: integer });
    type Person = ReturnType<typeof Person>;
    // the same as
    type Person = { name: string, age: number };


    npm i ts-cast


    Read ts-cast documentation on github:

    Getting Started

    Let's start with an example:


    import { integer, number, string, struct, tuple, array, toBe } from 'ts-cast';
    import v from 'validator';
    export const Person = struct({
      name: string,
      email: string.restrict(toBe(v.isEmail, "a valid email")),
    export const Coords = tuple(number, number);
    export const Book = struct({
      title: string,
      annotation: string.optional,
      year: integer,
      authors: array(Person),
      coords: Coords.optional,
    export type TPerson = ReturnType<typeof Person>;
    export type TCoords = ReturnType<typeof Coords>;
    export type TBook = ReturnType<typeof Book>;

    Then we can use defined types and their caster-s in this way:


    import { Person, TPerson, Book, TBook } from './schema';
    const me = Person({ name: "John Smith", email: "john@smith.com" });
    const meAgain: TPerson = {
      name: "John Smith",
      email: "john.smith@gmail.com", // but email will not be validated with validator.isEmail
    const myBook = Book({
      title: "My First Book",
      year: 2021,
      authors: [
        { name: 'Some Other Guy', email: 'other.guy@gmail.com' },
      coords: [1.2, 23.32]
    }, "myBook");
    const book: TBook = myBook;
    console.dir(book, { depth: null });

    TypeScript Analogy

    Primitive Types

    ts-cast TypeScript
    number number
    integer number
    string string
    boolean boolean
    nil null
    undef undefined


    import { integer } from 'ts-cast';
    const x = integer(10); // works
    const y = integer(Math.PI);  // throws TypeError
    const z = integet('10'); // also throws TypeError
    import { string } from 'ts-cast';
    const a = string('Hello Wordl!'); // works
    const b = string(''); // also works
    const c = string(null); // throws TypeError
    const d = string(20); // throws TypeError again

    Literal Types

    ts-cast TypeScript Comments
    value(V) V as const V extends number | string | boolean | symbol
    values(A, B, C, ...) A | B | C ... A, B, C ... extends number | string | boolean | symbol
    import { values } from 'ts-cast';
    const TrafficLight = values('red', 'yellow', 'green');
    const green = TrafficLight('green'); // works
    type TypeOfGreen = typeof green; // 'red' | 'yellow' | 'green'
    const wrong = TrafficLight('blue'); // throws TypeError

    Complex Types

    ts-cast TypeScript
    tuple(caster<T1>, caster<T2>, ...) [T1, T2, ...]
    array(caster<T>) T[]
    struct({ a: caster<A>, b: caster<B> }) { a: A, b: B }
    record(caster<K>, caster<V>) Record<K, V>

    Type Modifiers

    ts-cast TypeScript
    caster<T>.optional T | undefined
    caster<T>.default(v) x: T = v
    caster<T>.nullable T | null
    caster<T>.restrict(...) T

    Operations over Types

    ts-cast TypeScript
    union(caster<T1>, caster<T2>, ...) T1 | T2 | ...
    prod(caster<T1>, caster<T2>, ...) T1 & T2 & ...


    npm i ts-cast

    DownloadsWeekly Downloads






    Unpacked Size

    102 kB

    Total Files


    Last publish


    • dmitry.scheglov