What is the difference between using a Weak Map vs an Object with a closure to simulate private properties for a class?

Trying to wrap my head around this. Google Apps Script does not yet support private properties in a class, as alternative many posts suggest the use of Weak Map and a closure to approximate this behavior. Like this:

const myPrivate1 = (() => {
  const _private = new WeakMap();

  class myPrivate1{
    constructor({key, value}={}) {
      let obj = {};
      obj[key] = value;
      _private.set(this, obj);
    }

    getPrivate(key) {
      return _private.get(this)[key]
    }

    setPrivate({key, value}) {
      let priv_attrs = _private.get(this)
      priv_attrs[key] = value;
      _private.set(this, priv_attrs);
    }

  }

  return myPrivate1
})()

I've found that using an Object instead of the Weak Map behaves similarly. Like this:

const myPrivate2 = (() => {
  const _private = new Object();

  class myPrivate2{
    constructor({key, value}={}) {
      _private[key] = value;
    }

    getPrivate(key) {
      return _private[key]
    }

    setPrivate({key, value}) {
      _private[key] = value;  
    }

  }

  return myPrivate2
})()

to test this:

const testPrivate = () => {
  const testObj1 = new myPrivate1({key: 'id', value: 'xyz123'});
  const testObj2 = new myPrivate2({key: 'id', value: 'xyz123'});

  testObj1.setPrivate({key: 'name', value: 'Larry'});
  testObj2.setPrivate({key: 'name', value: 'Larry'})
  console.log(testObj1.getPrivate('name'));
  console.log(testObj2.getPrivate('name'));

  testObj1.setPrivate({key: 'id', value: 'abc987'});
  console.log(testObj1.getPrivate('id'));
  console.log(testObj2.getPrivate('id'));
  
  console.log(testObj1._private);
  console.log(testObj2._private);
}

Output:

2:40:50 PM Info Larry 2:40:50 PM Info Larry 2:40:50 PM Info abc987 2:40:50 PM Info xyz123 2:40:50 PM Info undefined 2:40:50 PM Info undefined

Can some explain the advantages of using a Weak Map vs Object?

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