A TypeScript Abstract class is a class which may have some unimplemented methods. These methods are called abstract methods. We can't create an instance of an abstract class. But other classes can derived from abstract class and reuse the functionality of base class.
TypeScript supports the abstract keyword for classes and their methods, properties, and accessors. An abstract class may have methods, properties, and accessors with no implementation, and cannot be constructed. See Abstract classes and methods and Abstract properties and accessors for more information. Mixins and Compositional Classes. Correct me if I'm wrong but it looks like @logProperty decorator defines property on prototype making things a bit wrong: as I can see running code from typescript playground this is a window object and then once you make several objects of type Person, changing the name for one of them will resolve in changing the name for all the others (since this property lives in prototype)?
TypeScript Interface vs Abstract Class
| Interface | Abstract Class |
|---|---|
| All members are abstract. | Some members are abstract and some are fully implemented. |
| Interfaces support multiple inheritances. | Abstract class does not support multiple inheritances. |
| TypeScript Interface has zero JavaScript code that means it is only available in TypeScript and does not produce any code in compiled JavaScript file. | Abstract class compile to JavaScript functions. |
| Interfaces are generic in nature. They can be implemented by any class for example IClone interface can be implemented by any class like business objects, database classes. | Abstract classes are related. For example ViewModelBase is an abstract, class then we know this class will only inherits by ViewModels. |
Syntax
In above example, we have created an abstract class. First method doWork is abstract and we put abstract keyword before the method name. Abstract method does not have any implementation. Second method workStarted has implementation and it is not an abstract method.
Constructor
In abstract class, we can write constructor which automatically executes when user creates a new instance of derived class. Constructor function always has same name constructor and it may have parameters. Below is the constructor example:
Constructor is always used to initialize variables values and object setup work. In above, we have a constructor of BaseEmployee which takes two parameters firstName and lastName. In constructor, we have assigned parameter values to our variables.
Derived Cass
In above example, we have created an abstract class BaseEmployee. We have one abstract method doWork which we do not provide any implementation. Employee class extends BaseEmployee class. In Employee class constructor we call BaseEmployee constructor using super method. super method is used to call base class constructor. super method takes the same parameters as defined in base class constructor.
Typescript Class Type
In last two lines, we have created an instance of Employee class and call doWork method.
Implement Interface
An abstract class can implement one or more interface. You can learn more about interfaces here. Below is the example of implementing interface by abstract class.
In above example, we have created two interfaces IName and IWork. Both interfaces are implemented by BaseEmployee abstract class by using implements keyword in highlighted line 10. Employee class extends BaseEmployee class. In line 32, we have created an emp variable of interface IWork and assign a new instance of Employee class. Now only member available in emp variable is doWork as emp variable data type is interface IWork.