Why I prefer using Type over Interface in TypeScript

TypeScript has gained significant popularity among developers for its ability to add static typing to JavaScript. One of the key features of TypeScript is its support for defining custom types and interfaces. While both types and interfaces serve similar purposes, I've found myself leaning towards using types over interfaces in my TypeScript projects. Here's why.

Clarity and Consistency

When it comes to defining types for variables, parameters, or return values, using the type keyword offers a straightforward and consistent syntax. Types provide a clear and concise way to define custom data structures, making the code easier to understand and maintain.

For example:

1type Point = {
2  x: number;
3  y: number;
4};

This syntax succinctly declares a type representing a point with x and y coordinates. It's immediately evident what properties are expected in an object of type Point.

Union and Intersection Types

Types in TypeScript offer more flexibility when it comes to creating union and intersection types. Union types allow you to combine multiple types into one, while intersection types enable you to create a new type by combining existing types.

1type StringOrNumber = string | number;
2type Point2D = { x: number; y: number };
3type Point3D = { z: number } & Point2D;

With types, you have the freedom to create complex type compositions that suit your specific requirements.

Extending and Combining Types

Using types allows for easier extension and combination of existing types. TypeScript provides the extends keyword to create new types based on existing ones, enabling code reuse and modularity.

1type Animal = {
2  name: string;
3  age: number;
4};
5
6type Dog = Animal & {
7  breed: string;
8};

This example demonstrates how to create a Dog type by extending the Animal type with additional properties specific to dogs.

Readability and Expressiveness

In many cases, I find that using types leads to more readable and expressive code. Types can be used to describe not only the shape of data but also their intended usage and constraints.

1type PositiveNumber = number & { __positive__: void };
2
3function squareRoot(x: PositiveNumber): number {
4  return Math.sqrt(x);
5}

Here, the PositiveNumber type ensures that only positive numbers are accepted as arguments to the squareRoot function, improving the clarity of its purpose.

Conclusion

While both types and interfaces have their place in TypeScript, I've personally found types to be more versatile and expressive in many scenarios. They offer clarity, consistency, and flexibility, allowing for the creation of robust and maintainable codebases. By embracing types, developers can leverage the full power of TypeScript to build better software.