text: class Foo {
      constructor(who) {
          this.me = who;
      }
      identify() {
          return "I am " + this.me;
      }
  }
  
  class Bar extends Foo {
      constructor(who) {
          super(who);
      }
      speak() {
          console.log("Hello, " + this.identify() + ".");
      }
  }
  
  let b1 = new Bar("b1");
  b1.speak(); // Hello, I am b1.