When to use Type and Interface in Typescript

Migrate from JavaScript to TypeScript for its robust type-checking capabilities, they often confront a common confusion: when to use interfaces and when to leverage types. Let’s unravel this mystery.

Understanding Interfaces in TypeScript

Interfaces in TypeScript facilitate the definition of contracts within your code, and they enforce these contracts across your objects, classes, and functions.

interface JottupUser {
    name: string;
    age: number;
    isActive?: boolean; // optional property
}

With the JottupUser interface, any object adhering to this contract must have a name and age, with an optional isActive property.

Delving into Types in TypeScript

Types, on the other hand, offer a way to define various data shapes, including primitive, union, and intersection types.

type JottupStatus = 'active' | 'inactive' | 'banned';

This defines a type where JottupStatus can only have one of the three string values mentioned.

Major Differences Between Interfaces and Types

• Extensibility: Interfaces are more extensible. They support multiple merged declarations, meaning you can declare an interface multiple times, and it will combine the definitions.
• Unions and Intersections: Types are more versatile in this regard. They support union and intersection types out of the box.
• Declaration Merging: Interfaces provide declaration merging, while types don’t.

When to Use Which?

Opt for interfaces when you need multiple merged declarations, or you’re defining the shape of an object or class. Types are a better choice for unions, intersections, tuple types, and more complex data structures.

Examples in Action

// Using Interface
interface JottupProfile {
    name: string;
    age: number;
}

const userJottup: JottupProfile = {
    name: "John",
    age: 25
}

// Using Type
type JottupAction = 'create' | 'update' | 'delete';

function performJottupAction(action: JottupAction) {
    // your logic here
}

The key takeaway is to understand the strengths and use cases of both constructs and leverage them according to the requirements of your project.

Mastering the nuances of TypeScript’s core features can greatly enhance your development workflow and codebase’s robustness. Whether you choose interfaces or types, ensure consistency across your project.