Seems like a cool trick that not too many people know about...Using PHP magic methods in JS, thanks to weird constructor semantics and Proxy. @assertchris

Env.js

class Env {
  constructor() {
    this.secrets = {};

    return new Proxy(this, {
      set: this.__set,
      get: this.__get,
    });
  }

  __set(obj, name, value) {
    return (obj.secrets[name] = value);
  }

  __get(obj, name) {
    return obj.secrets[name];
  }
}

// example

var env = new Env();

// can get + set secrets now
env.key = '5ec4e7s';