JSFiddle - React, Tailwind, and code Playground

HTML

<p id="log"></p>

JavaScript

function log(s) {
  document.getElementById("log").innerHTML+=s+"<br/>\n";
}

function Parent(x) {
  var private = x;
  Parent.prototype.get_private=function() {
    private_method();
    return private;
  };
  function private_method() {
    log("Private method on parent.");
  }
}

function Child(x,y) {
  Parent.call(this, x);
  var private = y;
  Child.prototype.get_private=function() {
    private_method();
    return private;
  };
  function private_method() {
    log("Private method on child.");
  }  
  this.get_parent_private=function() {
    return Parent.prototype.get_private.call(this);
  };
}

var p=new Parent(1);
log("p.get_private(): " + p.get_private());
var c=new Child(2,3);
log("c.get_private(): " + c.get_private());
log("c.get_parent_private(): " + c.get_parent_private());