factory.js

const createStudentCalsses =  function(...classes){
  console.log(classes.length)
  if(classes[0].length < 1) throw new Error("You should enroll in at least two classes")

  const privateObj =  {}

  privateObj.classes =  classes;

  const studentClasses = {
    getClasses(){ return privateObj.classes}
  }

  return studentClasses;
}

const student = new createStudentCalsses("math", "biology", "OS")
console.log(student.getClasses())