Catch-all API routes in NextJS - Mini Project: Build & Apply

Create a Catch-all API Route in Next.js

📖 Scenario: You are building a Next.js app that needs to handle API requests for multiple dynamic paths under one route.For example, you want to catch requests like /api/products/123, /api/products/123/reviews, or /api/products/123/reviews/456 with a single API route file.

🎯 Goal: Build a catch-all API route in Next.js that captures all sub-paths under /api/products and returns the path segments as JSON.

📋 What You'll Learn

Create a catch-all API route file named [...slug].ts inside app/api/products/

Extract the path segments from the request parameters

Return a JSON response with the captured path segments

Use Next.js 14+ App Router conventions with a GET handler

💡 Why This Matters

🌍 Real World

Catch-all API routes let you handle many dynamic URL paths with one file, useful for building flexible APIs in Next.js apps.

💼 Career

Understanding catch-all routes is important for Next.js developers building scalable backend APIs that respond to various dynamic paths.

1

Create the catch-all API route file

Create a file named [...slug].ts inside the app/api/products/ folder. Inside it, export an async function called GET that accepts a single parameter request and returns a JSON response with an empty array for slug.

NextJS

export async function GET(request: Request) {
  // Your code here
}

Hint

Start by creating the API route file and export a GET function that returns { slug: [] } as JSON.

2

Extract the catch-all route parameter

Inside the GET function, extract the slug parameter from the request URL using new URL(request.url).pathname. Then split the pathname by '/' and remove the first 4 segments to isolate the slug parts. Store the result in a variable called slug.

NextJS

import { NextResponse } from 'next/server';

export async function GET(request: Request) {
  const pathname = new URL(request.url).pathname;
  // Your code here
}

Hint

Use new URL(request.url).pathname to get the path, then split by '/' and slice from index 4 to get the slug array.

3

Handle the case when no slug is provided

Add a check to see if the slug array is empty. If it is empty, return a JSON response with { message: 'No slug provided' }. Otherwise, return the slug array as before.

NextJS

import { NextResponse } from 'next/server';

export async function GET(request: Request) {
  const pathname = new URL(request.url).pathname;
  const slug = pathname.split('/').slice(4);
  // Your code here
}

Hint

Check if slug.length === 0 and return a message JSON if true.

4

Complete the catch-all API route with proper export

Ensure the file exports the GET function as default export is not used. The file should be named [...slug].ts inside app/api/products/ and the GET function should handle the request as implemented.

NextJS

import { NextResponse } from 'next/server';

export async function GET(request: Request) {
  const pathname = new URL(request.url).pathname;
  const slug = pathname.split('/').slice(4);
  if (slug.length === 0) {
    return NextResponse.json({ message: 'No slug provided' });
  }
  return NextResponse.json({ slug });
}

// Your code here if needed

Hint

Make sure the GET function is exported correctly and the file is named [...slug].ts.

Practice

1. What does a catch-all API route file named [...slug].js in Next.js do?

easy

A. It catches all URL paths that match and provides the parts as an array in req.query.slug.

B. It only catches the root API path and ignores nested paths.

C. It catches only one specific URL path exactly matching slug.

D. It disables all API routes in the folder.

Solution

1. Step 1: Understand catch-all route naming

   In Next.js, files named with [...name].js catch all nested paths under that route.

2. Step 2: Check how parameters are passed

   The parts of the URL matched are passed as an array in req.query.name, here slug.

3. Final Answer:

   It catches all URL paths that match and provides the parts as an array in req.query.slug. -> Option A

4. Quick Check:

   Catch-all route = array in req.query [OK]

Hint: Catch-all uses [...name].js and returns array in req.query[name] [OK]

Common Mistakes:

• Thinking it catches only one path instead of many
• Expecting a string instead of an array in req.query
• Confusing catch-all with optional catch-all routes

2. Which of the following is the correct filename for a catch-all API route in Next.js?

easy

A. [slug].js

B. [...slug].js

C. slug.js

D. [slug...].js

Solution

1. Step 1: Recall catch-all route syntax

   Catch-all routes use three dots inside square brackets before the name, like [...slug].js.

2. Step 2: Compare options

   Only [...slug].js matches the correct syntax for catch-all routes.

3. Final Answer:

   [...slug].js -> Option B

4. Quick Check:

   Catch-all filename = [...name].js [OK]

Hint: Catch-all filenames always have three dots inside brackets [OK]

Common Mistakes:

• Using single brackets without dots for catch-all
• Placing dots outside brackets
• Missing brackets entirely

3. Given a catch-all API route file pages/api/[...params].js with this handler:

export default function handler(req, res) {
  res.json(req.query.params);
}

What will be the JSON response for a request to /api/a/b/c?

medium

A. "a/b/c"

B. {"params": "a/b/c"}

C. ["a", "b", "c"]

D. null

Solution

1. Step 1: Understand catch-all parameter passing

   The catch-all [...params] captures all path parts as an array in req.query.params.

2. Step 2: Check the handler response

   The handler returns req.query.params as JSON, so the response is the array of parts.

3. Final Answer:

   ["a", "b", "c"] -> Option C

4. Quick Check:

   Catch-all returns array of path parts [OK]

Hint: Catch-all returns array of URL parts in req.query [OK]

Common Mistakes:

• Expecting a string instead of an array
• Confusing JSON structure returned
• Not recognizing catch-all returns array

4. You wrote a catch-all API route pages/api/[...slug].js but when you request /api (no extra path), you get an error. What is the likely cause?

medium

A. You forgot to export the handler function.

B. The file name is incorrect; it should be [slug].js.

C. API routes cannot have dynamic segments.

D. Catch-all routes require at least one path segment; use optional catch-all [[...slug]].js instead.

Solution

1. Step 1: Understand catch-all vs optional catch-all

   Catch-all [...slug].js requires at least one path part; it does not match the base path alone.

2. Step 2: Identify fix for base path requests

   To handle base path /api with no extra parts, use optional catch-all [[...slug]].js.

3. Final Answer:

   Catch-all routes require at least one path segment; use optional catch-all [[...slug]].js instead. -> Option D

4. Quick Check:

   Catch-all needs path parts; optional catch-all handles empty [OK]

Hint: Use [[...name]].js for optional catch-all including empty path [OK]

Common Mistakes:

• Expecting catch-all to match empty path
• Misnaming the file without brackets
• Ignoring export of handler function

5. You want to create a catch-all API route that returns a JSON object with keys for each path part and their index, for example, for /api/a/b/c it returns {"0": "a", "1": "b", "2": "c"}. Which handler code inside pages/api/[...parts].js achieves this?

hard

A. export default function handler(req, res) {
const obj = {};
req.query.parts.forEach((p, i) => { obj[i] = p; });
res.json(obj);
}

B. export default function handler(req, res) {
res.json(req.query.parts.join(','));
}

C. export default function handler(req, res) {
res.json({ parts: req.query.parts });
}

D. export default function handler(req, res) {
res.json(req.query.parts.length);
}

Solution

1. Step 1: Understand the input and desired output

   The catch-all parameter parts is an array of path parts. We want to create an object with keys as indices and values as parts.

2. Step 2: Check which code builds the object correctly

   export default function handler(req, res) { const obj = {}; req.query.parts.forEach((p, i) => { obj[i] = p; }); res.json(obj); } loops over req.query.parts and assigns each part to the object with its index as key, then returns it as JSON.

3. Final Answer:

   export default function handler(req, res) { const obj = {}; req.query.parts.forEach((p, i) => { obj[i] = p; }); res.json(obj); } -> Option A

4. Quick Check:

   Loop parts to object with index keys = export default function handler(req, res) { const obj = {}; req.query.parts.forEach((p, i) => { obj[i] = p; }); res.json(obj); } [OK]

Hint: Use forEach to map array parts to object keys [OK]

Common Mistakes:

• Returning array or string instead of object
• Not looping to create object keys
• Returning length instead of parts