ts-transformer-typerep

A typescript custom transformer which enables a programmer to pull down type-level(compile time) information into value level(runtime).

import { typeRep, TypeKind } from 'ts-transformer-typerep';

function keys<T>(): string[] {
  const type = typeRep<T>();

  if (type.kind === TypeKind.Object) return type.properties.map(([key]) => key);
  else return [];
}

keys<{ x: 1, y: 2, z: 3 }>(); // ['x', 'y', 'z']

WARNING⚠️: This transformer is on experiment. It's not recommended to use this in product.

Installation

npm i -D ts-transformer-typerep

Check here and here to learn how to apply custom transformers.

Reference

Type TypeRep

Type representations are values that represent types. TypeRep is type of all type representation. Since typescript types can be classified in several groups, type representations are classified in groups, too.

| Type | Type Representation | |------|------------------------------------------------------------------------------------------| | any | AnyRep({ kind: TypeKind.Any }) | | number and its subtypes | NumberRep({ kind: TypeKind.Number, literal: number }) | | boolean and its subtypes | BooleanRep({ kind: TypeKind.Boolean, literal: boolean }) | | string and its subtypes | StringRep({ kind: TypeKind.String, literal: string }) | | symbol | SymbolRep({ kind: TypeKind.Symbol }) | | bigint and its subtypes | BigIntRep({ kind: TypeKind.BigInt, literal: bigint }) | | null | NullRep({ kind: TypeKind.null }) | | undefined | UndefinedRep({ kind: TypeKind.Undefined }) | | object | NonPrimitiveRep(({ kind: TypeKind.NonPrimitive }) | | unknown | UnknownRep({ kind: TypeKind.Unknown }) | | never | NeverRep({ kind: TypeKind.Never }) | | void | VoidRep({ kind: TypeKind.Void }) | | Any type constructed with Union operator but not never | UnionRep({ kind: TypeKind.Union, parts: TypeRep[] }) | | Any type constructed with Intersection operator | IntersectionRep({ kind: TypeKind.Intersection, parts: TypeRep[] }) | | Any object type with call signautre | FunctionRep({ kind: TypeKind.Function, parameters: TypeRep[], returnType: TypeRep }) |

Type TypeKind

TypeKind is type of values for discriminating different type representations. Different type representations are distinguished by its kind field, whose value is value of TypeKind.

const type = typeRep<number>();

if (type.kind === TypeKind.Number) console.log('It\'s a number type!');
else console.log('It\'s not a number type :(');

| Type | TypeKind | |------|----------| | any | Any | | number and its subtypes | Number | | boolean and its subtypes | Boolean | | string and its subtypes | String | | symbol | Symbol | | bigint and its subtypes | BigInt | | null | Null | | undefined | Undefined | | Any object type excluding subtypes of Object | NonPrimitive | | unknown | Unknown | | never | Never | | void | Void | | Any type constructed with Union operator but not never | Union | | Any type constructed with Intersection operator | Intersection | | Object | Object | | Any object type with call signature | Function |

Function typeRep<typeToPullDown>(): TypeRep

typeRep is a function to pull type level information into value level. It returns a type representation of given type.

typeRep<10>();
/**
{
  kind: TypeKind.Number,
  literal: 10
}
**/

WARNING⚠️: This function is not fully implemented yet, please refer to following 'Type Support Table' to check which types it supports.

Type Support Table

• Available(✅): A type is fully supported
• WIP(🚧): A type is partially supported
• Todo(📝): A type is planned to be supported

| Types | Current State | |---------|---------------| | Primitive types | ✅ | | Literal types | ✅ | | never/unknown/any/void | ✅ | | Polymorphic types | 🚧(Single type variable such as T, A only) | | Enums | 📝 | | Function types | ✅ | | Union types | ✅ | | Intersection types | ✅ | | Template literal types | 📝 | | Object types | ✅ |