Enums in JavaScript

enum.js

class Enum extends Function {
  static opts = { enumerable: true, writeable: true, configurable: false };
  constructor() {
    super();
    const names = (this.constructor+'').split('{')[1].split('}')[0].split(';').map(n => n.trim()).filter(n => n);
    names.forEach((name, i) => {
      Object.defineProperty(this.constructor, name.slice(1), { get: () => i, set: () => true, ...Enum.opts });
    });
    return this.constructor;
  }
}

const Day = new class extends Enum { $MONDAY; $TUESDAY; $WEDNESDAY; };
const day = Day.MONDAY;


function enum_(strings, ...values) {
  const str = strings.join('');
  const names = str.split(/[;.,]/g).map(n => n.trim()).filter(n => n);
  const e = Object.create(null);
  names.forEach((name, i) => e[name] = i);
  return e;
}

const Name = enum_`Fred, Cris, Harry, Megan`;
const personName = Name.Fred;

Syntax 1:

const Day = new class extends Enum { $MONDAY; $TUESDAY; $WEDNESDAY; };

Advantages: You get to say "new class extends Enum" which semantically sounds like an Enum.
Disadvantages: The first character of each constant is silent (but necessary to hack the class syntax in the way we are doing).

Syntax 2:

const Name = enum_`Fred, Cris, Harry, Megan`;

Advantages: Terser, straightforward
Disadvantages: Less "syntactically semantic", it's just a template tag function with a string. It's not a class or a type.