JSFiddle - React, Tailwind, and code Playground

JavaScript

function MyClass(){
    var foo = 'bar'; // private because of "scope"

    this.setfoo  = function(f) {
        foo = f;
    }

    this.getfoo = function() {
        return foo;
    }
}   

var instance = new MyClass();
console.log(instance.foo); // undefined
console.log(instance.getfoo()); // bar
instance.setfoo('a');
console.log(instance.getfoo()); // a