JS private property using function scopes.

private-property-constructor.js

const Person = (() => {
  const getName = privateProperties => privateProperties.name.split(' ')[0]
  const setName = (privateProperties, name) => {
    privateProperties.name = name
  }
  const getAge = privateProperties => privateProperties.age - 4
  const setAge = (privateProperties, age) => {
    privateProperties.age = age
  }

  return function (name = "Unnamed", age = 0) {
    const privateProperties = {
      name,
      age,
    }

    Object.defineProperties(this, {
      name: {
        get: getName.bind(null, privateProperties),
        set: setName.bind(null, privateProperties),
      },
      age: {
        get: getAge.bind(null, privateProperties),
        set: setAge.bind(null, privateProperties),
      },
    })
  }
})()

private-property.js

const make = (name = "Unnamed", age = 0) => {
  let privateName = name
  let privateAge = age

  return {
    get name() {
      return privateName.split(' ')[0]
    },
    get age() {
      return privateAge - 4
    },
    changeName(newName = "") {
      privateName = newName
    },
    getOld() {
      privateAge += 1
    },
  }
}