Which TypeScript feature allows for specifying types that cannot be extended or instantiated?

Understanding Abstract Classes in TypeScript

In the realm of TypeScript, one feature sets itself distinctly apart when it comes to specifying types that cannot be extended or instantiated, and that is Abstract Classes.

Abstract Classes are a fundamental component of TypeScript that allow developers to create classes that serve primarily as a base class for others to extend and build upon. Unlike regular classes, they can't be directly instantiated. In other words, they act as a blueprint for creating classes in TypeScript, but you can't create objects from them directly.

Here's a basic example to illustrate this concept:

abstract class Animal {
  constructor(public name: string) {}

  abstract makeSound(): void;

class Dog extends Animal {
  constructor(name: string) {

  makeSound() {

let myPet = new Dog('Rex');
myPet.makeSound(); // Outputs: 'Woof'

In the above code snippet, Animal is an abstract class that cannot be instantiated. It has a method makeSound() that is declared but not implemented. The Dog class extends Animal, provides an implementation for makeSound() and can be instantiated.

Remember, the primary goal of abstract classes in TypeScript is to be extended by other classes to encourage code reusability and to provide a proper and predictable structure for more complex entities.

In regards to best practices, abstract classes are best utilized in larger code bases, where grouping related entities and following consistent coding structures are vital. They can provide great service in setting consistent standards and reducing the potential for errors as application complexity grows.

On a concluding note, while interfaces, type aliases, and enumerations also play vital roles in TypeScript, they do not specifically cater to the use case of types that cannot be instantiated or extended. Abstract classes are unique in providing this functionality, hence making them an invaluable tool in the TypeScript utility belt.

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