How to make a private variable in Class and prevent add/delete it with freeze and seal function.

FreezeAndSeal.example.js

// ES6
// A normal object
class iPhoneX {
  secretName = 'iPhoneX'

  constructor(price) {
    this.price = price
  }

  setPrice = (value) => {
    if (typeof value !== 'number' && value >= 1000)
      throw new Error('Invalid price')

    this.price = value
  }
  
  getName = () => `Apple ${this.secretName}`
}

// Everything works well but
cons ipx = new iPhoneX(1000)
ipx.price = 300 // we don't want price can be set directly
// Even worse
ipx.setPrice = () => 'Override done.'
ipx.setPrice() // Override done
ipx.secretName = '' // ops, we dont want public this variable



// So Freeze function comes to help
function Product(price) {
  const secretName = 'iPhoneX'
  const setPrice = (value) => {
    if (typeof value !== 'number' && value >= 1000)
      throw new Error('Invalid price')

    price = value
  }
  
  const getPrice = () => price
  const getName = () => `Apple ${this.secretName}`
  
  return Object.freeze({setPrice, getPrice, getName})
}

const ipx = Product(1000) // no need 'new' keyword any more
console.log(ipx.getPrice()) // it's ok
ipx.setPrice(1100) // it's ok

ipx.price // undefined
ipx.setPrice = () => 'Try to re-assign' // it will not set
ipx.setPrice(2000) // still work
ipx.secretName // undefined

// Freeze function create a freezed object. Its properties and functions can not be re-assigned or deleted.
// We can do that with Seal function, but its properties and functions can be re-assigned.