Private atributes em JavaScript

Question

I'm new in JavaScript, so I am look for a way of create a private class to do a atrube and/or method to be unvisible of outside. But I need that in new syntax of class because is more easy I think. So there is two days that I'm try this. Look wich I achived to do:

'use strict';
//This class take all data private
function ExemplePrivate(value){
var _value = value;

this.set_value = function(val){
//Do you most to do validation before
_value = val;
}
this.get_value = function(){
//Do you should to do validation before
return _value;
}
}

//This class take all data public and extends the private class
class ClassPublic extends ExemplePrivate{
//adicional code
}

function runLoading(){ //Run as soon as loadin page
var cPublic = new ClassPublic('The child class has been <b>instanceid</b>');
document.querySelector('#p1').innerHTML = cPublic.get_value();
cPublic.set_value('The child class has been <b>update</b>');
document.querySelector('#p2').innerHTML = cPublic.get_value();

// Look that if try take _value atribute show as undefined
document.querySelector('#p3').innerHTML = `Result for <b>cPublic._value</b>: ${cPublic._value}.`;

Here you are my question:

Can I use my syntax in this way? Why?

Look the code in Sololearn view: https://code.sololearn.com/WCr4Dd182OY8

Answer 1

function ExemplePrivate() {
// code
}

FROM ABOVE:
extending directly from a constructor function isn't the right way. It's going to break the internal workings of how class works.

HOWEVER:
You could rather inherit from a normal function which returns a class. Making that function a higher order function capable of adding features to the class before extending from it into another class. e.g;

function modifyClass() {
return class ExemplePrivate {
// code
}
}

SOLUTION =>
By default classes have 'getters' and 'setters' accessor properties, which allow you to create private interfaces.

Some code shall we?

class User {
constructor(name) {
// invokes setter
this._name = name;
}

get name() {
return this._name;
}

set name(value) {
this._name = value;
}
}

let user = new User("Ben");
console.log(user.name); //=> Ben

BONUS TIP
Even though getters/setters are methods, they are invoked as data properties.