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How To Make A Class Implement An Interface In TypeScript?

Tim Mouskhelichvili
Tim Mouskhelichvili
2 minutes to read

When using object-oriented programming concepts in TypeScript, often a developer needs to make a class implement an interface. Luckily, this is easy to do.

To make a class implement an interface in TypeScript, you need to use the special implements keyword.

This article explains everything to know about implementing interfaces in TypeScript.

Let's get to it 😎.

typescript class implements interface

The definition

The implements keyword is used to make a class implement an interface in TypeScript.

Why should you make a class implement an interface, you may ask?

An interface is a contract that an object must follow.

By making a class implement an interface, you ensure that the class contains ALL the properties and methods defined inside the interface.

You can make a class implement an interface for several reasons:

  • When you have multiple classes that have the same behavior.
  • When you want to make a class more testable.
  • When you want to use specific design patterns that require it (for example, dependency injection).

How to make a class implement one interface?

To make a class implement one interface, use the implements keyword in the class definition.

Here is an example:

typescriptinterface IAnimal {
    name: string;
    eat: () => void;
}

class Dog implements IAnimal {

    public constructor(
        public name: string
    ) { }

    public eat () {
        console.log('The dog is eating.');
    }

}

const dog = new Dog('Fluffy');

// "The dog is eating."
dog.eat();

In this example, we first define the IAnimal interface.

Then, we make the Dog class implement the IAnimal interface.

Note: In this example, we use a constructor assignment to define a property inside the constructor.

How to make a class implement multiple interfaces?

In TypeScript, you can make a class implement multiple interfaces by passing a list of interfaces separated by commas to the class.

Here is an example:

typescriptinterface IAnimal {
    eat: () => void;
}

interface IDog {
    bark: () => void;
}

class Dog implements IAnimal, IDog {

    public bark () {
        console.log('The dog is barking.');
    }

    public eat () {
        console.log('The dog is eating.');
    }

}

const dog = new Dog();

// "The dog is eating."
dog.eat();

// "The dog is barking."
dog.bark();

The Dog class implements the IAnimal AND the IDog interfaces in this example.

Final thoughts

As you can see, making a TypeScript class implement an interface is easy.

Simply use the implements keyword, and voila.

typescript class implements interface

Here are some other TypeScript tutorials for you to enjoy:

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