Extend Functionality of a TypeScript Class with Decorators

Instructor: [0:00] We would create a function called the class degrader, which will take a generic T. It will take as an argument target which would be of type T. T will extend the new class with args of any type of array and return an object.

[0:23] This function will return a class that extends the target argument, and inside we will create a property called lesson number which will set the T value of one.

[0:43] We will create a class called lesson and inside that class, we'll add a property which is of type number called lesson number, and we will set it to a value zero. We'll instantiate this class by assigning it to a constant called lesson.

[1:06] We will console log this and go to our terminal to observe the zero. Now, using the add syntax we can decorate our class and modify its value. If we now go to our console and log out, we will see one.

[1:29] Similarly, if we change the lesson number in our decorator to two, we will see two. If we change it again to three, we would see three, and we can do four, and five, and so on.

[1:50] As a brief recap, we created a class decorator which took it generic T, and an argument of target which was a type T. That returned a class and extended that argument. We created a class of lesson and decorated it with the decorator to modify its value.