create class with readonly attribute.

mod1.js

const t = Symbol('ttt');

module.exports = class {
	constructor(name) {
		this[t] = name;
	}
	get name() {
		return this[t];
	}
	sayHello() {
		console.log(`Hello ${this.name}`);
	}
}

test.js

const Greeting = require('./mod1');
let m1 = new Greeting('Fillano');
m1.sayHello();//show 'Hello Fillano'
console.log(m1.name);//show 'Fillano'
m1.name = 'Allen';
console.log(m1.name);//still show 'Fillano'