Two ways to get private methods and data in JS.

privateMethodsAndData.js

"use strict"
console.log("––– Con –––")
function Con () {
  let privateData = 123

  private_makeMethodsPublic(this, [public_connect])

  function public_connect (username, password) {
    privateData = username + password
  }

  function private_makeMethodsPublic (context, methods) {
    methods.forEach(method => context[method.name] = method)
  }
}
const con = new Con()
console.log("Shows public methods:", con)
console.log("Public methods callable:", con.public_connect)
console.log("Private methods uncallable:", con.private_makeMethodsPublic)
console.log("No access to private state:", con.privateData)

console.log("––– Con2 –––")
const Con2 = publicizeClassMethods(class _Con {
  constructor () {
    this.privateData = 123
  }

  public_connect (username, password) {
    this.privateData = username + password
  }

  private_method (context, methods) {
  }
}, ["public_connect"])

function publicizeClassMethods (clas, methodNames) {
  const instance = new clas()
  return function () { return methodNames.reduce((obj, methodName) => (obj[methodName] = instance[methodName], obj), {}) }
}

const con2 = new Con2()
console.log("Shows public methods:", con2)
console.log("Public methods callable:", con2.public_connect)
console.log("Private methods uncallable:", con2.private_method)
console.log("No access to private state:", con2.privateData)