 Kai, let's talk about classes in TypeScript programming language. If you're already familiar with object-oriented languages such as C-Sharp, JavaScript and so on, you will notice that creating and using classes in TypeScript will be almost the same as in these object-oriented languages. So let's create a class. If we want to create a class, we need to use keyword class and after it, we need to put the name of our class. Let's call it book. Inside our class, we could put variables. For example, let's put variable title for our book, which will be string. You can also notice that you can have three types of accessibility level of variables inside your class and that is public, protected and private. So you can use those keywords to signify the accessibility level of your variables. I will use keyword public. So let's make one more variable, for example, publication year of our book and maybe let's say how to name it, let's say simply year, which will be a number. Also if you want, you can create a constructor, which starts with keyword constructor and let's provide few arguments for our constructor. Let's use title, which is going to be string and let's provide a year. Let's put this current year as default value for our argument. And as in many other object-oriented programming languages, we're going to use this keyword for title and year. We're going to say this dot title equals to title and this dot year equals to year. If you do not need to provide the constructor for your class, if you do not provide constructor implementation, the compiler will automatically generate one constructor that takes no parameters and initializes any instance members. And one last thing in the earlier version of JavaScript ECMA script 5. We do not have classes, but in the latest version ECMA script 6. We have classes, but we will talk about that subject in some other video. That's all for this lesson. Thanks for watching. Please don't forget to like, share and subscribe to my channel. That's all in this lesson.