5 questions found
How do you set up a Next.js project to use TypeScript?
Beginner
You can choose TypeScript when running create-next-app, or add it to an existing JavaScript project by installing TypeScript and its type definitions and renaming your files to use .ts or .tsx extensions, after which Next.js automatically detects and creates the necessary configuration file for you.
npx create-next-app@latest my-app --typescript
# Or add to an existing project
npm install --save-dev typescript @types/react @types/node
Real-world example
A developer starting a new project chooses the TypeScript option during setup, immediately getting helpful autocomplete and error checking as they write their first few components.
Common follow-ups: What happens automatically the first time you run the dev server after adding TypeScript?;Do you need to convert every file to TypeScript at once?
Next.js Project Setup & Configuration;Testing Next.js Applications
How do you properly type the props of a page component that receives dynamic route parameters?
Beginner
You define a type or interface describing the shape of the params object your page expects, matching the dynamic segments in your folder structure, and use it to type the props parameter of your page component, letting TypeScript catch mistakes if you try to access a parameter that does not exist.
type PageProps = {
params: Promise<{ id: string }>;
};
export default async function ProductPage({ params }: PageProps) {
const { id } = await params;
return <h1>Product {id}</h1>;
}
Real-world example
A product page properly types its params object, letting TypeScript immediately catch a typo if a developer accidentally tries to access a parameter name that does not match the actual dynamic route segment.
Common follow-ups: Why is the params object typed as a Promise in recent versions of Next.js?;How do you type searchParams for a page that reads query string values?
Dynamic Routes & Catch-All Segments;Next.js Project Setup & Configuration
How do you type the data returned from an API call inside a server component to get proper autocomplete and error checking?
Intermediate
You define an interface describing the expected shape of the API response, and use it as the return type for your data fetching function, letting TypeScript check that your JSX correctly uses only the fields that actually exist on that data, catching mistakes before the code ever runs.
interface Product {
id: string;
name: string;
price: number;
}
async function getProduct(id: string): Promise<Product> {
const res = await fetch(`https://api.example.com/products/${id}`);
return res.json();
}
Real-world example
A product page defines a clear Product interface matching its API response, immediately catching an error if a developer tries to display a field, like a discount, that does not actually exist on the product data.
Common follow-ups: What happens if the actual API response does not match the defined interface?;Should you validate the shape of API responses at runtime in addition to typing them?
Data Fetching;Database Integration with Next.js
How would you create strongly typed server actions that validate their input and return a predictable, typed result?
Advanced
You define types for both the expected form data shape and the return value of your server action, often combining this with a runtime validation library like zod to ensure the data actually matches your types at runtime, giving both compile time safety and runtime protection against unexpected input.
import { z } from 'zod';
const schema = z.object({ email: z.string().email() });
type FormState = { error?: string; success?: boolean };
export async function subscribe(prevState: FormState, formData: FormData): Promise<FormState> {
const result = schema.safeParse({ email: formData.get('email') });
if (!result.success) {
return { error: 'Invalid email address' };
}
return { success: true };
}
Real-world example
A newsletter signup feature combines TypeScript types with zod validation in its server action, catching both type mismatches during development and invalid data at runtime before it ever reaches the database.
Common follow-ups: What is the relationship between TypeScript types and runtime validation libraries like zod?;How do you type the state managed by the useActionState hook?
Server Actions & Mutations;Form Handling & Validation in Next.js
How do you set up strict TypeScript settings for a Next.js project, and what benefits does this provide for a growing codebase?
Advanced
You enable strict mode in your tsconfig.json file, which turns on a comprehensive set of stricter type checking rules, such as requiring explicit handling of potentially null or undefined values, catching more mistakes at compile time and making a large, growing codebase significantly easier to maintain safely over time.
// tsconfig.json
{
"compilerOptions": {
"strict": true,
"noUncheckedIndexedAccess": true
}
}
Real-world example
A growing startup enables strict mode early in their project's life, catching several potential null reference bugs during development that would have otherwise caused confusing crashes for real users months later.
Common follow-ups: What specific checks does strict mode actually enable?;Is it difficult to add strict mode retroactively to an older, large codebase?
Next.js Project Setup & Configuration;Testing Next.js Applications