SerializeType utility for converting a type to JSON

SerializeType.ts

// credit @colinhacks
// https://github.com/remix-run/remix/pull/1254

type JSONPrimitives = string | number | boolean | null;
type NonJSONPrimitives = undefined | Function | symbol;

export type SerializeType<T> = T extends JSONPrimitives
  ? T
  : T extends undefined
  ? undefined
  : T extends { toJSON(): infer U }
  ? U
  : T extends []
  ? []
  : T extends [any, ...any[]]
  ? {
      [k in keyof T]: T[k] extends NonJSONPrimitives
        ? null
        : SerializeType<T[k]>;
    }
  : T extends (infer U)[]
  ? SerializeType<U>[]
  : {
      [k in keyof T as T[k] extends NonJSONPrimitives
        ? never
        : k]: SerializeType<T[k]>;
    };