TypeScript Utilities

• Prettify

  Takes an object type and makes the hover overlay more readable.

  type Prettify<T> = {
    [K in keyof T]: T[K];
  } & {};

• Maybe

  Returns a union of the type and a potentially missing value, such as undefined or null. It's using NoInfer to provide a more readable hover overlay.

  type Maybe<T> = NoInfer<T | undefined | null>;

• NonEmptyArray

  Represents an array that has to have at least 1 element in it.

  type NonEmptyArray<T> = [T, ...Array<T>];

• UniqueElements

  Returns a union of the unique elements of the array.

  type UniqueElements<T extends unknown[]> = T[number];

• DuplicateElements

  Returns a union of the duplicate elements found in the array.

  type DuplicateElements<
    T extends unknown[],
   Seen = never,
    Duplicates = never,
  > = T extends [infer First, ...infer Rest]
   ? First extends Seen
     ? DuplicateElements<Rest, Seen, Duplicates | First>
     : DuplicateElements<Rest, Seen | First, Duplicates>
   : Duplicates;

• UniqueArray

  Represents an array that can contain only unique elements. Using branded types to provide a more readable hover overlay.

  declare const brand: unique symbol;
  type ValidElements<T> = [T] & { [brand]: "ValidElements" };
  
  type UniqueArray<T extends unknown[]> =
    DuplicateElements<T> extends never ? T : ValidElements<UniqueElements<T>>;

• AnyFn

  Represents a function that can take any number and type of arguments and return any. Sometimes TypeScript forces you to use it in generics.

  type AnyFn = (...args: any[]) => any;