TypeScript Type vs. Interface: What’s the Difference?

In TypeScript, we use two primary types of class definitions to define the structure of our classes: interfaces and types. These two concepts are often used interchangeably in TypeScript; however, there are some subtle differences between them that you should understand before making any assumptions about when you should use one over the other.

In this article, we’ll dive into what makes them different and why it might be essential to know which one to use when writing your classes in TypeScript.

Main Difference

When it comes to programming, there are often many different ways to accomplish the same task. In the case of TypeScript, there are two ways to define types – using the Type keyword or an interface. So, what’s the difference between these two approaches?

The answer lies in how each is used. The Type keyword is used to create a new type that can be used anywhere within your code. An interface, on the other hand, defines a contract that must be adhered to by any class that implements it.

In terms of syntax, a Type is defined using the keyword followed by a curly brace enclosed list of properties and their types. An interface looks similar but uses the keyword interface instead of type. Other than that, they look very similar. So, which should you use? It depends on your needs.

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What is TypeScript Type?

TypeScript is a programming language developed and maintained by Microsoft, a company known for its software products. It is a strict syntax superset of JavaScript and offers optional static typing. It was created to help developers create larger applications and transpile them to JavaScript. In this post, we will discuss what TypeScript types are and what they do. We will also be talking about interfaces about types in TypeScript.

What is Interface?

An interface is a syntactical contract that an entity must conform to. In other words, an interface defines the rules that a class or object must follow. If a class or object does not follow these rules, it will not be able to compile.

Interfaces are used to define types in TypeScript. For example, let’s say we have an animal interface and two classes, Dog and Cat, which implement this interface. We can declare that Dog implements Animal with the following syntax.

Difference Between TypeScript Type and Interface?

The difference between a Type and an Interface in TypeScript is that a Type can be used to describe an object and its values, while an Interface can only be used to describe an object. In addition, a Type can be defined within the same file as it is used, while an Interface must be declared in a separate file. Finally, types can be aliased, while interfaces cannot. Alias means that two different types share the same name.
An example of when you might want to use a type instead of an interface is if you are defining multiple constructors for your class or struct. If you define them as methods on the interface, they will all share the same name and create collisions. If you define them on their Type of object, then they will have their names, and there won’t be any collisions.

Basic Understanding of Types and Interfaces

To understand the difference between Type and Interface in TypeScript, we must first understand what they are. A Type in TypeScript is a structure that defines the type of an object. This means that it defines the properties and methods that are available on that object.

On the other hand, an Interface is a description of an object type. It only describes what properties and methods are available on that object but doesn’t define them.

Overview of A Type: TypeScript Type vs. Interface

In TypeScript, a type is a way of categorizing values that have specific characteristics in common. For example, all strings have the same methods and properties, so they can be said to belong to the string type.

Similarly, all numbers have specific shared methods and properties, so they can be said to belong to the number type. It’s important to note that although JavaScript doesn’t have a formal type system as TypeScript does, it does use types behind the scenes in its language features. It also has an implicit conversion between different types (for example, when you pass 123 as an argument for an expected number).

Overview of An Interface: TypeScript Type vs. Interface

An interface is a code-based contract that defines how a class will communicate with other classes. It’s a bit like a set of instructions that say, if you want to talk to this class, here’s how you do it. The interface can specify which properties and methods are available for use and their signatures and return types.

The following snippet shows an example of an interface’s appearance in code. Notice the export keyword at the top? That specifies that any external script or application can use this interface.

Overriding an Interface (Extending)

To override an interface, we must first extend it. We use the extends keyword followed by the interface name to do this. Once we have extended the interface, we can add, remove, or change any of its members.

For example, let’s say we have an interface with a single property called name. If we want to add another property called favorite color, we would just need to create a new member in our class and call it favorite color like so: //Interface: public interface MyInterface { public string Name { get; set; } } //Class: public class MyClass : MyInterface { public string Name { get; set; } public string FavoriteColor { get; set; } } The member FavoriteColor is now also part of the interface because we have added it to the class that implements it.

In addition, if we wanted to take away the Name property from the interface and only keep FavoriteColor, we could simply delete its declaration in the interface definition: //Interface: public interface MyInterface { public string FavoriteColor { get; set; } }

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Implementation Details: TypeScript Type vs. Interface

So, what’s the difference between a Type and an Interface in TypeScript? First, let’s take a look at how they are defined. A Type is defined using the type keyword, while an Interface is defined using the interface keyword.

As you can see, they are similar in structure, but there are some essential differences. The most significant difference is that TypeScript Types may implement interfaces, while types cannot. The other significant difference is that a Type may specify any number of properties or methods (even no properties or methods). Still, an Interface must have precisely one property or method declared.


A typeScript is a powerful tool that can help you write better code. But with great power comes great responsibility. TypeScript can make your code more reliable and easier to understand. But used incorrectly, it can make your code more difficult to read and maintain.

About James Smith

A freelance writer specializing in business, finance, and technology. He has studied these subjects and spends a lot of time developing content to assist explain complex content for the average individual.

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