Interface in TypeScript

Last updated on 2 Feb, 2023

An interface describes the structure of an object. We create an interface using interface keyword. interface keyword exists only in TypeScript, not in vanilla JavaScript.

Let us define the structure of a car object using interface.

interface Car {
  model: string;
  year: number;

The interface contains the name of the properties present in the object and also the type of each properties.

We can also add details about methods present in the object. Say, we have a method show() in the car object. The method accepts a parameter, message which is a string. Also, the method returns nothing. Here is how we give the details of the method in our existing interface.

interface Car {
  model: string;
  year: number;

  show(message: string): void;

Now we have an interface. The advantage now is that, when we declare a variable, say car1, we can set the type of car1 as Car. That makes car1 to accept only an object that follows the Car interface structure.

let car1: Car;

At a later point, when we assign an object to car1, it should follow all the structure of Car interface as shown below:

car1 = {
  model: "BMW",
  year: 2023,
  show: (message) => {
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Joby Joseph
Web Architect