JSFiddle - React, Tailwind, and code Playground

JavaScript

var Calculator = function() {
    var priv = 0;

    return {
        changePriv: function() {
            priv++;
        },
        printPriv: function() {
            document.writeln(priv + '<br/>');
        }
    }
}

document.writeln("myCalc:<br/>")
var myCalc = Calculator();
myCalc.printPriv();
myCalc.changePriv();
myCalc.printPriv();

document.writeln("myOtherCalc:<br/>")
var myOtherCalc = Calculator();
myOtherCalc.printPriv();
myOtherCalc.changePriv();
myOtherCalc.changePriv();
myOtherCalc.printPriv();

document.writeln("myNewCalc:<br/>")
var myNewCalc = new Calculator();
myNewCalc.printPriv();
myNewCalc.changePriv();
myNewCalc.changePriv();
myNewCalc.printPriv();

document.writeln(myCalc instanceof Calculator);
document.writeln(myOtherCalc instanceof Calculator);
document.writeln(myNewCalc instanceof Calculator);