TypeScript support in Next.js - Mini Project: Build & Apply

TypeScript support in Next.js

📖 Scenario: You are building a simple Next.js app that uses TypeScript to ensure your code is safe and clear. You want to create a typed component that shows a greeting message with a name.

🎯 Goal: Build a Next.js functional component using TypeScript that accepts a name prop of type string and displays a greeting message.

📋 What You'll Learn

Create a TypeScript interface for the component props

Use the interface to type the component props

Create a functional component that returns a greeting message

Export the component as default

💡 Why This Matters

🌍 Real World

Using TypeScript in Next.js helps catch errors early and makes your code easier to understand and maintain.

💼 Career

Many companies use Next.js with TypeScript for building scalable web apps, so knowing this skill is valuable for frontend developer roles.

1

Create a TypeScript interface for props

Create a TypeScript interface called GreetingProps with one property name of type string.

NextJS

// Your code here

Hint

Use the interface keyword to define the shape of the props object.

2

Create a typed functional component

Create a functional component called Greeting that takes props typed as GreetingProps and returns a <div> with the text Hello, {props.name}!.

NextJS

interface GreetingProps {
  name: string;
}

// Your code here

Hint

Use the function keyword and specify the props type after the parameter name.

3

Export the component as default

Add a default export statement for the Greeting component.

NextJS

interface GreetingProps {
  name: string;
}

function Greeting(props: GreetingProps) {
  return Hello, {props.name}!;
}

// Your code here

Hint

Use export default followed by the component name.

4

Use the component in a Next.js page

Create a Next.js page component called HomePage that imports Greeting and uses it with the prop name set to "Next.js Learner". Export HomePage as default.

NextJS

interface GreetingProps {
  name: string;
}

function Greeting(props: GreetingProps) {
  return Hello, {props.name}!;
}

export default Greeting;

// Your code here

Hint

Import the Greeting component and use it inside the HomePage component's return statement.

Practice

1. What happens when you add a tsconfig.json file to a new Next.js project?

easy

A. You must manually configure TypeScript settings in Next.js.

B. Next.js automatically detects TypeScript and configures the project.

C. Next.js disables JavaScript support.

D. The project will not run until you install extra plugins.

Solution

1. Step 1: Understand Next.js TypeScript auto-configuration

   Next.js detects tsconfig.json and sets up TypeScript automatically without extra steps.

2. Step 2: Confirm no manual setup needed

   Developers do not need to manually configure TypeScript; Next.js handles it.

3. Final Answer:

   Next.js automatically detects TypeScript and configures the project. -> Option B

4. Quick Check:

   TypeScript auto-config = A [OK]

Hint: Add tsconfig.json and Next.js auto-configures TypeScript [OK]

Common Mistakes:

• Thinking manual config is required
• Believing JavaScript support is disabled
• Assuming extra plugins are mandatory

2. Which file extension should you use for a React component with TypeScript in Next.js?

easy

A. .js

B. .ts

C. .tsx

D. .jsx

Solution

1. Step 1: Identify file extension for React components with TypeScript

   React components with JSX syntax and TypeScript use the .tsx extension.

2. Step 2: Differentiate from plain TypeScript files

   Files without JSX use .ts, but components need .tsx.

3. Final Answer:

   .tsx -> Option C

4. Quick Check:

   React + TypeScript = .tsx [OK]

Hint: Use .tsx for React components with TypeScript [OK]

Common Mistakes:

• Using .ts for components with JSX
• Using .js or .jsx without TypeScript
• Confusing .tsx with .jsx

3. Given this Next.js TypeScript component, what is the rendered output?

type Props = { name: string };

export default function Greeting({ name }: Props) {
  return <h1>Hello, {name}!</h1>
}

Used as <Greeting name="Alice" />

medium

A. Hello, Alice!

B. Hello, {name}!

C. Error: Missing prop type

D. Hello, !

Solution

1. Step 1: Understand prop typing and usage

   The component expects a prop name of type string and uses it inside JSX.

2. Step 2: Substitute the prop value in JSX

   When called with name="Alice", it renders Hello, Alice! inside an h1.

3. Final Answer:

   <h1>Hello, Alice!</h1> -> Option A

4. Quick Check:

   Prop value replaces {name} = C [OK]

Hint: Props typed and passed render as expected in JSX [OK]

Common Mistakes:

• Thinking JSX shows literal {name}
• Assuming missing props cause error here
• Ignoring prop substitution

4. What is wrong with this Next.js TypeScript page component?

export default function Page({ id }: { id: number }) {
  return <p>ID: {id.toUpperCase()}</p>
}

medium

A. Next.js does not support inline prop typing.

B. Missing explicit return type causes a compile error.

C. Props object should be typed as any.

D. Using toUpperCase() on a number causes a compile-time error.

Solution

1. Step 1: Analyze prop type and method usage

   The prop id is a number, but toUpperCase() is a string method.

2. Step 2: Identify compile-time error cause

   Calling toUpperCase() on a number causes a compile-time error because numbers don't have this method.

3. Final Answer:

   Using toUpperCase() on a number causes a compile-time error. -> Option D

4. Quick Check:

   Number.toUpperCase() = error [OK]

Hint: Check method matches prop type to avoid compile-time errors [OK]

Common Mistakes:

• Assuming missing return type causes error
• Thinking inline typing is unsupported
• Using any type unnecessarily

5. You want to create a Next.js API route with TypeScript that returns JSON with a typed message. Which is the correct way to type the request and response parameters?

import type { NextApiRequest, NextApiResponse } from 'next';

export default function handler(req: ???, res: ???) {
  res.status(200).json({ message: 'Success' });
}

hard

A. req: NextApiRequest, res: NextApiResponse<{ message: string }>

B. req: any, res: any

C. req: Request, res: Response

D. req: NextApiRequest, res: NextApiResponse

Solution

1. Step 1: Import correct types from Next.js

   Use NextApiRequest for request and NextApiResponse with a generic type for response data.

2. Step 2: Specify response JSON shape

   Typing NextApiResponse<{ message: string }> ensures the response JSON matches the expected structure.

3. Final Answer:

   req: NextApiRequest, res: NextApiResponse<{ message: string }> -> Option A

4. Quick Check:

   Typed API response = D [OK]

Hint: Use NextApiResponse with generic for typed JSON response [OK]

Common Mistakes:

• Using generic Request/Response from Node or browser
• Not typing response JSON shape
• Using any type losing type safety