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TypeScript Interface vs Class

TypeScript Interface vs Class

Are you curious about the differences between a TypeScript interface and class? If so, read on to learn more about how each one works.

The key difference between an interface and class is that an interface gives the structural building block for a grouping of related values or functions, while a class implements this structure by creating objects to use those values or functions. In TypeScript, interfaces are defined with the keyword ‘interface’ whereas classes are declared using either ‘class’ or ‘constructor’ keywords.

With all this in mind, let’s dive into further details on how each of these two differ and why they are important when dealing with setting up structures for our project!

TypeScript Interfaces

Interfaces in TypeScript provide a powerful and flexible way to define contracts within your code. Essentially, interfaces are like a blueprint that describes the structure of an object.

When you create an interface in TypeScript, you can dictate the required properties and their respective types that must be implemented in order to adhere to that interface. This can help catch errors earlier in the development process and make your code easier to understand and maintain.

Additionally, interfaces can be extended and used to create more complex data structures. Overall, interfaces are an essential tool in TypeScript for building scalable and reliable code.

TypeScript Classes

TypeScript is a superset of JavaScript that provides class-based object-oriented programming features. It follows a structure that is quite similar to that of Java and C++.

Classes are a core feature of TypeScript, used to encapsulate data and functionality. They also facilitate polymorphism through inheritance and interfaces, improving code reuse and making it more scalable. The syntax is intuitive, and with the help of reference materials, it is easy to grasp the concept of creating and utilizing classes in TypeScript. By implementing classes, developers can create complex applications with ease.

Overall, TypeScript classes are a powerful tool to make development faster and more efficient, providing a solid foundation for the future of web programming.

TypeScript Interface vs Class: At a Glance

AspectTypeScript InterfaceTypeScript Class
DefinitionIt’s a structure that defines the contract in your application and sets the behavior a certain entity should have.It’s a blueprint for creating objects. A class encapsulates data and functions that manipulate that data.
PurposeInterfaces are used for type-checking and establishing contracts for classes, objects, and functions.Classes are used to create objects and instantiate a specific instance of an object. They can include constructors, methods, fields, properties, and implement interfaces.
ImplementationInterfaces are purely a compile-time construct and have no implementation details.Classes can have implementation details. They can contain constructors, methods, fields, etc.
InstantiationYou cannot instantiate an interface directly. It’s used as a type that classes can implement.You can instantiate a class to create a new object.
ExtensibilityInterfaces can extend other interfaces, creating a combined interface.Classes can extend other classes and implement interfaces.
Accessibility ModifiersInterfaces do not use accessibility modifiers.Classes can use accessibility modifiers (private, public, protected).
RuntimeInterfaces do not exist at runtime, they are used by the TypeScript compiler to understand the shape of an object.Classes exist at runtime and can be used to create new instances.
MethodsInterfaces can only declare methods, they can’t provide an implementation.Classes can declare and implement methods.
PropertiesInterfaces can have properties, but they cannot be initialized.Classes can have properties and they can be initialized.

Examples of TypeScript Interface

interface Animal {
    name: string;
    age: number;
    isPet: boolean;
    speak(): void;

class Dog implements Animal {
    name: string;
    age: number;
    isPet: boolean;

    constructor(name: string, age: number, isPet: boolean) { = name;
        this.age = age;
        this.isPet = isPet;

    speak(): void {
        console.log( + " says: Woof!");

let myDog: Animal = new Dog('Rex', 5, true);
myDog.speak(); // Outputs: Rex says: Woof!

In this example, the Animal interface describes what shape an object should have. It must have a name property of type string, an age property of type number, a isPet property of type boolean, and a speak method of type void.

The Dog class implements the Animal interface, meaning it adheres to the structure outlined by the interface. It has a name, age, isPet property and speak method. The method speak outputs a console log with the name of the dog and a bark sound.

We then create an instance of the Dog class and assign it to a variable of type Animal. This ensures that myDog adheres to the Animal interface.

Please note that interfaces don’t exist at runtime. They are a compile-time construct used by TypeScript to ensure type safety.

Examples of TypeScript Class

class Employee {
    private firstName: string;
    private lastName: string;
    private age: number;

    constructor(firstName: string, lastName: string, age: number) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;

    public getFullName(): string {
        return `${this.firstName} ${this.lastName}`;

    public isAdult(): boolean {
        return this.age >= 18;

let john = new Employee('John', 'Doe', 30);
console.log(john.getFullName()); // Outputs: John Doe
console.log(john.isAdult());     // Outputs: true

In this example, the Employee class has three private properties: firstName, lastName, and age. These properties are set through the constructor when a new instance of Employee is created.

The class has two public methods: getFullName() and isAdult(). The getFullName() method returns the full name of the employee by concatenating firstName and lastName. The isAdult() method checks if the employee is an adult by checking if the age property is 18 or more.

An instance of the Employee class is then created, named john, with the new keyword. The getFullName() and isAdult() methods are then called on this instance, and the results are output to the console.

This is a fundamental use of classes in TypeScript, and similar patterns can be seen in other object-oriented languages.

Comparing Interfaces and Classes in TypeScript

In the world of TypeScript, understanding the differences between interfaces and classes is crucial. At their core, interfaces serve as a blueprint for the structure of a class, providing a guideline for the properties and methods that it should contain. On the other hand, classes are where the rubber meets the road – they implement the structure outlined by the interface, creating an object that can be instantiated and used in your program.

Definition and Purpose

Interfaces serve as a way of declaring contracts within your code and with external code, making sure that objects and classes adhere to a specific structure.

On the other hand, classes serve as blueprints for creating objects that share the same configuration of properties and methods. They encapsulate data and functions that manipulate that data, making it easier to work with complex code structures.


Interfaces are great for defining the types of properties and methods that an object should have, without actually implementing them. This makes it easier to create interchangeable components, as any object that conforms to an interface can be used in its place.

Classes, on the other hand, allow for the actual implementation of properties and methods, making them more useful for creating objects that can be instantiated and used throughout your codebase.


Interfaces provide a way to define the shape of an object or function, without the need to worry about implementation details.

On the other hand, classes allow developers to bundle together properties, methods, and constructors to create instances for use within the code.

Inheritance and Extension

While interfaces offer a chain of contracts to adhere to and can be extended by other interfaces, they lack the ability to contain details about implementation.

On the other hand, classes can implement interfaces to enforce rules for the class and can also extend other classes, inheriting properties and methods.

Access Modifiers

One of the main differences lies in access modifiers. Interfaces don’t have access modifiers, which means all of its members are public by default.

In contrast, classes allow developers to use access modifiers like public, private, and protected to restrict access to certain properties or methods. This provides more control over the data that is exposed and how it can be manipulated.


An interface lays out the blueprint of an object, but you cannot create an instance of it. On the other hand, a class is a blueprint for an object and you can use the ‘new’ keyword to create an instance of it.

While both serve different purposes, it’s important to understand their differences to determine the right approach for your project. Whether you choose to use an interface or a class for your object instantiation, make sure to consider the scope and functionality of your project.

Advantages of Using TypeScript Interfaces & Classes

As the world of web development continues to evolve and become increasingly complex, TypeScript emerges as a powerful tool that simplifies the development process significantly. Using TypeScript’s interfaces and classes offers numerous benefits to both developers and companies alike.

One of its biggest benefits is the prevention of runtime errors by detecting issues during development. TypeScript’s static typing helps improve code quality, making it easier to read, debug, and manage at scale.

With interfaces, developers can define the shapes of objects and classes, making it easier to reason about the code with its self-documenting nature.

By utilizing TypeScript’s interfaces and classes, companies can improve productivity, reduce production errors, and create scalable applications and libraries.

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