We can extend the Interfaces in TypeScript to include other interfaces. This helps us to create a new interface consisting of definitions from the other interfaces. Extending interfaces gives us more flexibility in how we define our interfaces and reuse the existing interfaces.
Typescript is capable of defining Interfaces for functions. In this tutorial, we will learn how to define an interface for function types and use it.
The Interface in TypeScript defines the Shape of an object. i.e. it specifies what properties & methods a given object can have and their corresponding value types. TypeScript interfaces are abstract types. They do not contain any code. An object, function, or class that implements the interface must implement all the properties specified in the interface. They are similar to type alias. Both allow us to name a type and use it elsewhere in the code.
Readonly is a typescript keyword that makes the property read-only in a class, interface, or type alias. We make a property read only by prefixing the property as readonly. We can assign a value to the read only property only when initializing the object or within a constructor of the class. Any other assignments will result in a compiler error.
Optional Properties are those properties that are not mandatory. In the example below the person object name is usually mandatory but age may not be. When we create a person object without assigning a value to age the compiler throws age is missing in a type error. To solve this problem, we need to mark the property as optional.
