Why do we need to use abstract keyword for classes and their methods in TypeScript?

In TypeScript, the abstract keyword is used for both classes and their methods to define a level of abstraction that enforces a certain structure and behavior upon any derived classes. The primary reasons for using the abstract keyword in TypeScript are as follows:

1. Defining a Base Class: An abstract class serves as a base class from which other classes may derive. It provides a common definition and structure that derived classes must follow. Abstract classes cannot be instantiated directly, which means you cannot create an instance of an abstract class. This enforces the idea that an abstract class is meant only to be a foundation for other classes, not to be used on its own[2][3][4][9][10][11].

2. Enforcing Implementation of Methods: Abstract methods within an abstract class do not contain an implementation. Instead, they define the signature of the method without including a method body. This means that any class deriving from the abstract class must implement these abstract methods, ensuring that certain behaviors are implemented across all subclasses. This is particularly useful for defining a consistent interface or behavior that all derived classes must adhere to[2][3][4][9][10][11].

3. Code Reusability and Maintenance: Abstract classes allow for a high level of code reusability. By defining common methods and properties in an abstract class, you can avoid code duplication across derived classes. This not only makes the codebase more maintainable but also ensures consistency in the implementation of common functionality. Additionally, changes to the abstract class are propagated to all derived classes, simplifying maintenance[2][3][4][10][11].

4. Flexibility and Design: Using abstract classes and methods allows for more flexible and sophisticated designs. It enables the creation of a hierarchy of classes that share a common structure while allowing for specific implementations to differ. This is particularly useful in complex systems where you need to enforce a certain architecture without limiting the specific implementation details of derived classes[2][3][4][10][11].

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