⚡ Response Helpers in Next.js

Next.js provides Response Helpers in API routes (pages/api/) and middleware to handle HTTP responses efficiently. These helpers make it easy to send JSON responses, set headers, manage redirects, and handle errors.

📌 1. Sending JSON Responses (res.json())

Use res.json() to send structured JSON data in API routes.

🔹 Example: Basic JSON Response

javascript
export default function handler(req, res) {  res.status(200).json({ message: "Hello from Next.js API!" });}

✅ Sends a JSON response with status 200 OK

📌 2. Setting HTTP Status Codes (res.status())

You can set custom HTTP status codes using res.status().

🔹 Example: Handling Success & Errors

javascript
export default function handler(req, res) {  if (req.method !== "GET") {    return res.status(405).json({ error: "Method Not Allowed" }); // 405  }  res.status(200).json({ message: "Success" });}

✅ Returns 405 Method Not Allowed for non-GET requests
✅ Returns 200 OK for successful GET requests

📌 3. Redirecting Users (res.redirect())

Redirect users from API routes using res.redirect().

🔹 Example: Redirect to Another Page

javascript
export default function handler(req, res) {  res.redirect(302, "/new-page");}

✅ Redirects the user to /new-page (Temporary Redirect: 302)

📌 4. Setting Custom Headers (res.setHeader())

Use res.setHeader() to add custom headers.

🔹 Example: Caching & Security Headers

javascript
export default function handler(req, res) {  res.setHeader("Cache-Control", "s-maxage=3600, stale-while-revalidate");  res.setHeader("X-Custom-Header", "NextJS");  res.status(200).json({ message: "Headers Set" });}

✅ Sets cache & custom headers for better performance

📌 5. Sending Plain Text Responses (res.send())

Use res.send() to return raw text instead of JSON.

🔹 Example: Sending a Simple Message

javascript
export default function handler(req, res) {  res.status(200).send("Hello, Next.js!");}

✅ Useful for API responses that don't need JSON

📌 6. Handling Errors (try/catch)

Use error handling to gracefully respond to failures.

🔹 Example: Handling API Errors

javascript
export default async function handler(req, res) {  try {    const response = await fetch("https://api.example.com/data");    if (!response.ok) throw new Error("Failed to fetch data");    const data = await response.json();    res.status(200).json(data);  } catch (error) {    res.status(500).json({ error: error.message });  }}

✅ Returns 500 Internal Server Error if the API request fails

📌 7. Streaming Responses (res.write())

Stream large responses using res.write() and res.end().

🔹 Example: Streaming Response

javascript
export default function handler(req, res) {  res.setHeader("Content-Type", "text/plain");  res.write("Chunk 1\n");  res.write("Chunk 2\n");  res.end("Done\n");}

✅ Useful for streaming large data sets

📌 8. Returning HTML Responses (res.send())

Send raw HTML content as a response.

🔹 Example: Returning HTML

javascript
export default function handler(req, res) {  res.setHeader("Content-Type", "text/html");  res.send("<h1>Welcome to Next.js</h1>");}

✅ Useful for generating server-side rendered HTML

📌 9. Response Helpers in Middleware (app/middleware.js)

You can modify responses inside middleware before reaching a page.

🔹 Example: Redirect Users in Middleware

javascript
import { NextResponse } from "next/server";export function middleware(req) {  if (!req.cookies.token) {    return NextResponse.redirect(new URL("/login", req.url));  }}

✅ Redirects users to /login if they are not authenticated

🚀 Summary: Response Helpers in Next.js