Private class props

function makeIndex() {
    return Math.random().toString(12).substring(2, 12);
}

function Awesome() {
    Object.defineProperty(this, 'index', {
        writable: false,
        configurable: false,
        value: makeIndex()
  });
}

Awesome.prototype.getIndex = function() {
    return this.index;
}

Awesome.prototype.setIndex = function(value) {
    this.index = value;
}

// or

const myPrivateMethod = Symbol("myPrivateMethod");
const myPrivateProperty = Symbol("myPrivateProperty");

class MyClass {
  constructor(){
    this[myPrivateProperty] = makeIndex();
  }
  
  [myPrivateMethod](){
    return `ID: ${this[myPrivateProperty]}!!!`;
  }
  
  hello() {
    console.log(this[myPrivateMethod]()); 
  }
}