Types vs Interfaces in TypeScript: A Clear Guide for Developers

If you have been working with TypeScript for a while, you have probably come across both types and interfaces. At first glance, they look very similar. Both let you define the shape of objects and give structure to your code. But when should you use one over the other? Let’s break it down in a way that is simple and practical.

What is a Type?

A type in TypeScript is like a label you attach to a value. It tells the compiler what kind of data to expect. With type, you can describe:

• Objects
• Primitives like string, number, boolean
• Unions
• Intersections
• Functions

Here is an example:

type User = {
  id: number
  name: string
}

type Status = "active" | "inactive" | "suspended"

In the above code, User describes an object structure while Status is a union of string literals.

Types are very flexible because they allow combinations. You can use unions, intersections, and mapped types to express complex structures.

What is an Interface?

An interface also defines the shape of an object. It is most commonly used to describe objects and classes.

Example:

interface User {
  id: number
  name: string
}

This looks almost identical to the earlier type example. Where interfaces shine is in extending and merging.

Key Differences

Extension

• Interfaces can extend other interfaces.
• Types can extend other types using intersections.

interface Person {
  id: number
}

interface Employee extends Person {
  role: string
}

type Animal = { species: string }
type Dog = Animal & { breed: string }

Both achieve the same outcome, but the syntax differs.

Declaration Merging

Interfaces support something called declaration merging. If you declare the same interface twice, TypeScript combines them.

interface Car {
  brand: string
}

interface Car {
  model: string
}

const myCar: Car = {
  brand: "Toyota",
  model: "Corolla"
}

With type, this is not possible.

Use Cases

• Use type when you need unions, intersections, or more advanced type expressions.
• Use interface when you are working with objects, classes, or want to take advantage of declaration merging.

Which One Should You Use?

In practice, both types and interfaces are valid choices. The TypeScript team itself has said that you should not stress too much about which to use. If you are modeling complex combinations of data, types might feel more natural. If you are designing the shape of objects or classes, interfaces might make more sense.

A good rule of thumb is:

• Start with an interface when describing objects.
• Reach for types when you need more flexibility.

Final Thoughts

Types and interfaces in TypeScript are not rivals. They are tools that overlap in many areas but also have unique strengths. The more you work with them, the more natural it becomes to decide which one to use in a given situation.

So next time you are writing TypeScript, do not overthink it. Choose the one that feels right for the problem you are solving, and remember that both are first class citizens in the language.

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