The simplest possible `maybe` implementation in TypeScript

maybe.ts

type None = null | undefined;

export class Maybe<T> {
  private _value: T | undefined;

  public constructor(value: T | None) {
    this._value = value === null ? undefined : value;
  }
  
  public value(): T | undefined {
    return this._value;
  }

  public map<U>(fn: (value: T) => U | None): Maybe<U> {
    return new Maybe<U>(typeof value === 'undefined' ? undefined : fn(this._value));
  }
}

export const maybe = <T>(value: T | None) => new Maybe<T>(value);