JavaScript private methods with ES6 classes vs IIFE's and closure

constructor1.js

// private methods with constructor functions without ES6 classes
const Student = (function() {
  function privateMethod() {
    console.log('Private method...');
  }

  return function(name, age) {
    this.name = name;
    this.age = age;
    privateMethod();
  }
})();

const mustafa = new Student('Mustafa', 42);
console.log(mustafa);

/*
Private method...
{ name: 'Mustafa', age: 42 }
*/

mustafa.privateMethod(); // TypeErro

constructor2.js

// private methods with constructor functions using ES6 classes
class Student {
  constructor(name, age) {
    this.name = name;
    this.age = age;
    this.#privateMethod();
  }

  #privateMethod() {
    console.log('Private method...');
  }
}

const mustafa = new Student('Mustafa', 42);
console.log(mustafa);

/*
Private method...
{ name: 'Mustafa', age: 42 }
*/

mustafa.#privateMethod(); // SyntaxError