<script>
     class MyBook
     {
          // constructor at the class
          constructor(name)
          {
               // this.variable name = ...
               // this is to create a variable for the class

               // create variables for the class
               this.Name = name; // the variable contains text
               this.Author = "";   // the variable contains text
               this.Price = 0;      // the variable contains a number
               this.Valuta = '';    // the variable contains text

               // create a variable for the class
               this.MyInfo = // the variable contains a set of properties
               {
                    // property set
                    PagesCount: 90,
                    HasPictures: true
               };
          }

          // function at the class
          ShowMyMessage(title)
          {
               alert(title + " " + this.Name + " " + this.MyInfo.PagesCount);
          }
     }

     // create a class object
     var obj1 = new MyBook("Mathematics");

     // call the function at the class
     obj1.ShowMyMessage("My Book");
     // On the screen we will see "My Book Mathematics 90"
</script>

<script>
     class MyBook
     {
          // function at the class
          Calculate()
          {
               this.Price = 100;
          }
     }

     // create a class object
     var obj1 = new MyBook;

     // call the function at the class
     obj1.Calculate();

     // display the variable at the class
     alert(obj1.Price);
     // On the screen we will see 100
</script>

<script>
     class MyBook
     {
          // function at the class
          static Show()
          {
               alert("Hello!");
          }
     }

     // call a static function on a class
     MyBook.Show();
     // On the screen we will see Hello!
</script>

<script>
     // create a class object
     var obj1 = new MyBook("Mathematics"); // Error! Uncaught ReferenceError: MyBook is not defined

     // class definition
     class MyBook
     {
          // class constructor
          constructor(name)
          {
               this.Name = name;
          }
     }
</script>

<script>
     // define an unnamed class
     var myClass1 = class
     {
          // constructor at the class
          constructor(name)
          {
               this.Name = name;
          }

          // function at the class
          ShowMyMessage()
          {
               alert(this.Name);
          }
     };

     // create a class object
     var obj1 = new myClass1("Fantastic");

     // call the function at the class
     obj1.ShowMyMessage();
     // On the screen we will see "Fantastic"
</script>

<script>
     // create an unnamed class object
     var obj1 = new class
     {
          // constructor at the class
          constructor(name)
          {
               this.Name = name;
          }

          // function at the class
          ShowMyMessage()
          {
               alert(this.Name);
          }
     }("Fantastic");

     // call the function at the class
     obj1.ShowMyMessage();
     // On the screen we will see "Fantastic"
</script>

<script>
     // class definition
     class Cat
     {
          // constructor at the class
          constructor()
          {
          }

          // function at the class
          Say()
          {
               alert("Meow");
          }
     }
    
     // class Tiger inherited from class Cat
     class Tiger extends Cat
     {
          // constructor at the class
          constructor()
          {
               // call the constructor at the base class
               super();
          }

          // function at the class
          Say()
          {
               // call the function at the base class
               super.Say();

               alert("Snarl");
          }
     }

     // create a class object
     var obj1 = new Tiger();
     obj1.Say();
     // On the screen we will see "Meow" "Snarl"
</script>

class Tiger extends Cat
{
     // constructor at the class
     constructor()
     {
          // call the constructor at the base class
          super();
     }
}

class Tiger extends Cat
{
     // constructor at the class
     constructor()
     {
          // Error! The base class constructor was not invoked
          // Uncaught ReferenceError: Must call super constructor in derived class before accessing 'this' or returning from derived constructor
     }
}