tsdef

tsdef

TypeScript common patterns shortcuts definitions snippets utility gist library

Get Started

npm install -D tsdef

or

yarn add -D tsdef

How to Use

import { Nullable, NonNull } from 'tsdef';

const nullableString: Nullable<string> = null; // ok

const nonNullString: NonNull<string | null> = null; // error

Documentation (Source Code)

export type nil = null | undefined;

export type Nilable<T> = T | nil;
export type Nullable<T> = T | null;
export type Undefinable<T> = T | undefined;

export type MaybeNil<T> = T | nil;
export type MaybeNull<T> = T | null;
export type MaybeUndefined<T> = T | undefined;
export type MaybePromise<T> = T | Promise<T>;
export type MaybeArray<T> = T | T[];
export type MaybeAsReturnType<T> = T | ((...args: any) => T);

// removes both null or undefined from T
export type NonNil<T> = T extends nil ? never : T;

// removes null from T
export type NonNull<T> = T extends null ? never : T;

// removes undefined from T
export type NonUndefined<T> = T extends undefined ? never : T;

// make all properties nilable
export type NilableProps<T> = { [P in keyof T]?: T[P] | nil };

// make all properties nullable
export type NullableProps<T> = { [P in keyof T]: T[P] | null };

// make all properties undefinable
export type UndefinableProps<T> = { [P in keyof T]?: T[P] | undefined };

// make all properties non nilable
export type NonNilProps<T> = { [P in keyof T]-?: NonNil<T[P]> };

// make all properties non null
export type NonNullProps<T> = { [P in keyof T]: NonNull<T[P]> };

// make all properties non undefined
export type NonUndefinedProps<T> = { [P in keyof T]-?: NonUndefined<T[P]> };

export type RequiredProps<T> = { [P in keyof T]-?: T[P] };

// string | number | symbol
export type AnyKey = keyof any;

// matches any functions
export type AnyFunction = (...args: any) => any;

// matches any constructors
export type AnyConstructor = new (...args: any) => any;

// matches classes
export interface AnyClass {
  prototype: any;
  new (...args: any): any;
}

// matches prototypes
export interface AnyPrototype {
  constructor: any;
}

// matches any objects
export interface AnyObject {
  [key: string]: any;
  [key: number]: any;
}

// matches objects with string keys
export interface AnyObjectWithStringKeys {
  [key: string]: any;
}

// matches objects with number keys
export interface AnyObjectWithNumberKeys {
  [key: number]: any;
}

// without some keys
export type ExcludeKeys<T, K extends AnyKey> = Omit<T, K>;

// values of object
export type ValueOf<T> = T[keyof T];

// get a property
export type Property<T, K> = K extends keyof T ? T[K] : never;

// get keys with values of given type
export type KeyOfType<T, U> = {
  [P in keyof T]-?: T[P] extends U ? P : never
}[keyof T];

// get keys with values of given sub type
// For some reason, this works and KeyOfType doesn't when U = undefined
export type KeyOfSubType<T, U> = {
  [P in keyof T]-?: U extends T[P] ? P : never
}[keyof T];

// make some keys optional
export type WithOptionalKeys<T, K extends keyof T> = Omit<T, K> &
  Partial<Pick<T, K>>;

// make some keys nilable
export type WithNilableKeys<T, K extends keyof T> = Omit<T, K> &
  NilableProps<Pick<T, K>>;

// make some keys nullable
export type WithNullableKeys<T, K extends keyof T> = Omit<T, K> &
  NullableProps<Pick<T, K>>;

// make some keys undefinable
export type WithUndefinableKeys<T, K extends keyof T> = Omit<T, K> &
  UndefinableProps<Pick<T, K>>;

// make some keys non nil
export type WithNonNilKeys<T, K extends keyof T> = Omit<T, K> &
  NonNilProps<Pick<T, K>>;

// make some keys non null
export type WithNonNullKeys<T, K extends keyof T> = Omit<T, K> &
  NonNullProps<Pick<T, K>>;

// make some keys non undefined
export type WithNonUndefinedKeys<T, K extends keyof T> = Omit<T, K> &
  NonUndefinedProps<Pick<T, K>>;

// make all properties optional recursively including nested objects.
// keep in mind that this should be used on json / plain objects only.
// otherwise, it will make class methods optional as well.
export type DeepPartial<T> = {
  [P in keyof T]?: T[P] extends Array<infer I>
    ? Array<DeepPartial<I>>
    : DeepPartial<T[P]>
};

// first object properties excluding common keys with second object
export type DiffObjects<T, U> = Omit<T, keyof U>;

// union of two objects
export type UnionObjects<
  T extends AnyObject,
  U extends AnyObject
> = DiffObjects<T, U> &
  { [P in keyof T & keyof U]: T[P] | U[P] } &
  DiffObjects<U, T>;

// similar to Object.assign
export type OverwriteProps<T, U> = U & DiffObjects<T, U>;

// get arguments type
export type Arguments<T extends AnyFunction> = Parameters<T>;

// get arguments type
export type FirstArgument<T extends AnyFunction> = T extends (
  arg: infer A,
  ...args: any
) => any
  ? A
  : never;

// get return value type
export type Return<T extends AnyFunction> = ReturnType<T>;

// get return type if a function, otherwise return itself
export type MaybeReturnType<T> = T extends (...args: any[]) => infer R ? R : T;

// get instance type of class
export type InstanceOf<T extends AnyConstructor> = InstanceType<T>;

// get promise return type
// PromisedType<Promise<T>> = T
export type PromisedType<T extends Promise<any>> = T extends Promise<infer R>
  ? R
  : never;

// get promise return type if promise, otherwise return itself
// MaybePromisedType<T | Promise<T>> = T
export type MaybePromisedType<T> = T extends Promise<infer R> ? R : T;

// get promise return type
export type MaybeAsyncReturnType<T extends AnyFunction> = MaybePromisedType<
  ReturnType<T>
>;

// get array item type
export type ItemType<T extends any[]> = T extends Array<infer I> ? I : never;

// get thunk for type
export type Thunk<T> = () => T;

// get thunk or self
export type MaybeThunk<T> = T | Thunk<T>;

// get return type of thunk
export type Unthunk<T extends Thunk<any>> = T extends Thunk<infer R>
  ? R
  : never;

// get return type if thunk, otherwise get self
export type MaybeUnthunk<T> = T extends Thunk<infer R> ? R : T;

// get inferred type of array item or return value or promised value
export type Unpack<T> = T extends Array<infer I>
  ? I
  : T extends (...args: any) => infer R
  ? R
  : T extends Promise<infer P>
  ? P
  : T;

// InheritClass<C1, C2>: class C1 extends C2 {}
export type InheritClass<C1 extends AnyClass, C2 extends AnyClass> = {
  prototype: OverwriteProps<C2['prototype'], C1['prototype']>;
  new (...args: ConstructorParameters<AnyClass>): OverwriteProps<
    C2['prototype'],
    C1['prototype']
  >;
} & OverwriteProps<C2, C1>;

// return True if T is not null nor undefined, otherwise return False
// test null and undefined separately to prevent side effect from args distribution
export type IsNonNil<T, True, False = never> = null extends T
  ? False
  : undefined extends T
  ? False
  : True;

// return True if T is not null, otherwise return False
export type IsNonNull<T, True, False = never> = null extends T ? False : True;

// return True if T is not undefined, otherwise return False
export type IsNonUndefined<T, True, False = never> = undefined extends T
  ? False
  : True;

// return True if T is `never`, otherwise return False
// wrap with array to prevent args distributing
export type IsNever<T, True, False = never> = [T] extends [never]
  ? True
  : False;

// return True if T is `any`, otherwise return False
export type IsAny<T, True, False = never> = (
  | True
  | False) extends (T extends never ? True : False)
  ? True
  : False;

// return True if T is `unknown`, otherwise return False
export type IsUnknown<T, True, False = never> = unknown extends T
  ? IsAny<T, False, True>
  : False;

// return True if T strictly includes U, otherwise return False
export type StrictlyIncludes<T, U, True, False = never> = Exclude<
  U,
  T
> extends never
  ? (IsAny<T, 1, 0> extends 1
      ? True
      : (IsAny<U, 1, 0> extends 1
          ? False
          : (IsUnknown<T, 1, 0> extends 1 ? IsUnknown<U, True, False> : True)))
  : False;

// tests and returns True if they are equal, False otherwise.
// wrap with array and do both ways to prevent args distrubition
export type AreStrictlyEqual<T, U, True, False = never> = StrictlyIncludes<
  T,
  U,
  1,
  0
> extends 1
  ? StrictlyIncludes<U, T, True, False>
  : False;

// tests and returns True if both objects have same keys, False otherwise.
export type HaveSameKeys<T, U, True, False = never> = (
  | Exclude<keyof T, keyof U>
  | Exclude<keyof U, keyof T>) extends never
  ? True
  : False;

// https://github.com/Microsoft/TypeScript/issues/26051
export type Exact<T, X extends T> = T &
  { [K in keyof X]: K extends keyof T ? X[K] : never };
// U extends Exact<{ [K in keyof T]-?: (v: T[K]) => any }, U>

Contribute

Pull Requests are welcome!
Just try to be consistent with existing naming conventions and coding styles.
Names must be concise, easy to read, and precisely descriptive.
I've setup prettier, so make sure your codes are auto formatted according to my prettier setup.

License

MIT License