Edit in JSFiddle

var output = function (msg) {
    var n = document.createElement('div');
    n.innerText = msg;
    document.getElementById('message').appendChild(n);
};

(function () {
    "use strict";
    class Person {
        constructor(name, age) {
            this.name = name;
            this.age = age;
        }

        getName() {
            return this.name;
        }

        sayHello() {
            return 'Hello I\'m ' + this.getName();
        }
    }

    var alice = new Person('Alice', 7);
    output(alice.sayHello());

    class Employee extends Person {
        constructor(name, age, salary) {
            super(name, age);
            this.salary = salary;
        }

        sayHello() {
            return super.sayHello() + ' (salary:' + this.salary + ')';
        }
    }

    var bob = new Employee('Bob', 25, 1234);
    output(bob.sayHello());
  
    // 'this' is not lexical.
    var hello = bob.sayHello;
    try {
      output(hello());
    } catch (e) {
      output('Error: ' + e);
    }
}());

<div id="message"></div>