Are you new to TypeScript and wondering how to effectively use interfaces and types? You’ve come to the right place! This beginner’s guide will walk you through everything you need to know about TypeScript interfaces and types, helping you write cleaner and more efficient code.

What Are Types in TypeScript?

In TypeScript, types are a way to define the shape of data. They allow you to specify the exact type of variables, function parameters, and object properties. By using types, you can catch errors early and ensure that your code behaves as expected.

How to Declare Types

Here’s how you can declare types for variables:

let age: number = 25;
let name: string = "John Doe";
let isActive: boolean = true;

Using Type Annotations in Functions

Type annotations can also be used in function parameters and return values:

function add(a: number, b: number): number {
  return a + b;
}

Understanding TypeScript Interfaces

Interfaces in TypeScript are used to define the structure of an object. They are a powerful way to define custom types and ensure that objects adhere to specific contracts.

How to Declare Interfaces

Here’s how you can declare an interface:

interface User {
  name: string;
  age: number;
  email?: string; // Optional property
}

Implementing Interfaces

You can use the interface to type-check objects:

let user: User = {
  name: "Jane Doe",
  age: 28,
  email: "jane.doe@example.com",
};

Differences Between Types and Interfaces

While both types and interfaces can be used to define the shape of an object, there are subtle differences:

• Declaration Merging: Interfaces allow for declaration merging, whereas types do not.
• Union Types: Types can represent union types (type Status = "success" | "error";), but interfaces cannot.
• Extensibility: Interfaces are generally more extensible and are preferred for defining object shapes.

When to Use Types vs. Interfaces

• Use Interfaces when you need to define the structure of an object or class.
• Use Types when you need to define primitives, unions, or tuples.

Practical Examples

Using Types for Union Types

type Status = "success" | "error" | "loading";

let currentStatus: Status = "loading";

Extending Interfaces

interface Person {
  name: string;
  age: number;
}

interface Employee extends Person {
  employeeId: number;
}

let employee: Employee = {
  name: "Alice",
  age: 30,
  employeeId: 1234,
};

Conclusion

Understanding how to use TypeScript interfaces and types is crucial for writing robust and maintainable code. Interfaces are ideal for defining object structures, while types are versatile for defining primitives and unions. By leveraging both, you can enhance type safety and catch errors early in the development process.

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