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0.0.0-6 • Public • Published


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.


npm i -D ts-transformer-typerep

Check here to learn how to apply custom transformers.


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[] })

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

Function typeRep<typeToPullDown>(): TypeRep

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

  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
Polymorphic types 🚧(Single type variable such as T, A only)
Enums 📝
Function types
Union types
Intersection types
Template literal types 📝
Object types

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