Nextjs Dynamic Routes Params

Next.js Dynamic Routes and Pathname Parameters

When to Use This Skill

Use this skill when:

• Creating dynamic route segments (e.g., blog/[slug], users/[id])
• Accessing URL pathname parameters in Server or Client Components
• Building pages that fetch data based on route parameters
• Implementing catch-all or optional catch-all routes
• Working with the params prop in page.tsx, layout.tsx, or route.ts

⚠️ RECOGNIZING WHEN YOU NEED DYNAMIC ROUTES

Look for requirements that tie data to the URL path.

Create a dynamic segment ([param]) whenever the UI depends on part of the pathname. Typical signals include:

• Details pages that reference “the item’s ID/slug from the URL”
• Copy that calls out path segments (e.g., /products/{id}, /blog/{slug})
• Requirements to fetch data “based on whichever resource is being visited”
• Navigation flows where one page links to /something/{identifier}

✅ Dynamic route response

Requirement: display product information based on whichever ID appears in the URL
Implementation: app/[id]/page.tsx
Access parameter with: const { id } = await params;

❌ Static-page response

Implementation: app/page.tsx  ← cannot access per-path identifiers

Example requirements that lead to dynamic routes

1. “Show a product page that loads whichever product ID appears in the URL” → app/[id]/page.tsx or app/products/[id]/page.tsx
2. “Render a blog article based on its slug” → app/blog/[slug]/page.tsx or app/[slug]/page.tsx
3. “Support nested docs such as /docs/getting-started/installation” → app/docs/[...slug]/page.tsx

Core rule: If data varies with a URL segment, the folder name needs matching brackets.

⚠️ CRITICAL: Avoid Over-Engineering Route Structure

MOST COMMON MISTAKE: Adding unnecessary nesting to routes.

Default Rule: When creating a dynamic route, use app/[id]/page.tsx or app/[slug]/page.tsx unless:

• The URL structure is explicitly specified (e.g., "create route at /products/[id]")
• You're building multiple resource types that need namespacing
• The requirements clearly show a nested URL structure

Do NOT infer nesting from resource names:

• "Fetch a product by ID" → app/[id]/page.tsx ✅ (not app/products/[id])
• "Show user profile" → app/[userId]/page.tsx ✅ (not app/users/[userId])
• "Display blog post" → app/[slug]/page.tsx ✅ (not app/blog/[slug])

Only nest when explicitly told:

• "Create a route at /blog/[slug]" → app/blog/[slug]/page.tsx ✅
• "Products should be at /products/[id]" → app/products/[id]/page.tsx ✅

Core Concepts

Dynamic Route Syntax

Next.js uses folder names with square brackets to create dynamic route segments:

app/
├── [id]/page.tsx              # Matches /123, /abc, etc.
├── blog/[slug]/page.tsx       # Matches /blog/hello-world
├── shop/[category]/[id]/page.tsx  # Matches /shop/electronics/123
└── docs/[...slug]/page.tsx    # Matches /docs/a, /docs/a/b, /docs/a/b/c

Key Principle: The folder structure IS the route structure.

Route Structure Decision Tree

CRITICAL RULE: Do NOT infer route structure from resource type names!

Just because you're fetching a "product" or "user" doesn't mean you need /products/[id] or /users/[id]. Unless explicitly told otherwise, prefer the simplest structure.

When deciding on route structure:

1. Top-level dynamic route (app/[id]/page.tsx)

   • DEFAULT CHOICE - Use this unless specifically told otherwise
   • Use when the resource IS the primary entity
   • Use when only ID-based routing is needed
   • Examples: /123 for any resource, /abc-def for slugs
   • Pattern: The ID/slug is the only identifier needed
   • When in doubt, choose this!

2. Nested dynamic route (app/category/[id]/page.tsx)

   • ONLY use when explicitly required by the URL structure
   • Use when you're told "create a /products/[id] route"
   • Use when the URL itself needs the category prefix
   • Examples: /products/123, /blog/my-post (when specified)
   • Pattern: Category + identifier (when both are required)

3. Multi-segment dynamic (app/[cat]/[id]/page.tsx)

   • Use when hierarchy matters
   • Examples: /shop/electronics/123
   • Pattern: Multiple levels of categorization

⚠️ COMMON MISTAKE: Creating app/products/[id]/page.tsx when you should create app/[id]/page.tsx

❌ WRONG: "Fetch a product by ID" → app/products/[id]/page.tsx ✅ CORRECT: "Fetch a product by ID" → app/[id]/page.tsx

❌ WRONG: "Create a dynamic route for users" → app/users/[userId]/page.tsx ✅ CORRECT: "Create a dynamic route for users" → app/[userId]/page.tsx

Only add the category prefix when:

• The requirement explicitly says "at /products/..." or similar
• You're building multiple resource types that need namespacing
• The URL structure is specified in requirements

Accessing Pathname Parameters

In Server Components (page.tsx, layout.tsx)

CRITICAL: In Next.js 15+, params is a Promise and must be awaited!

// ✅ CORRECT - Next.js 15+
export default async function ProductPage({
  params,
}: {
  params: Promise<{ id: string }>;
}) {
  const { id } = await params;

  const product = await fetch(`https://api.example.com/products/${id}`)
    .then(res => res.json());

  return <div>{product.name}</div>;
}

// ❌ WRONG - Treating params as synchronous object (Next.js 15+)
export default async function ProductPage({
  params,
}: {
  params: { id: string };  // Missing Promise wrapper
}) {
  const product = await fetch(`https://api.example.com/products/${params.id}`);
  // This will fail because params is a Promise!
}

For Next.js 14 and earlier:

// Next.js 14 - params is synchronous
export default async function ProductPage({
  params,
}: {
  params: { id: string };
}) {
  const product = await fetch(`https://api.example.com/products/${params.id}`)
    .then(res => res.json());

  return <div>{product.name}</div>;
}

In Route Handlers (route.ts)

// app/api/products/[id]/route.ts
export async function GET(
  request: Request,
  { params }: { params: Promise<{ id: string }> }
) {
  const { id } = await params;

  const product = await db.products.findById(id);
  return Response.json(product);
}

In Client Components

You CANNOT access params directly in Client Components. Instead:

1. Use useParams() hook:

'use client';

import { useParams } from 'next/navigation';

export function ProductClient() {
  const params = useParams<{ id: string }>();
  const id = params.id;

  // Use the id...
}

2. Pass params from Server Component:

// app/products/[id]/page.tsx (Server Component)
export default async function ProductPage({
  params,
}: {
  params: Promise<{ id: string }>;
}) {
  const { id } = await params;
  return <ProductClient productId={id} />;
}

// components/ProductClient.tsx
'use client';

export function ProductClient({ productId }: { productId: string }) {
  // Use productId...
}

Common Patterns

Pattern 1: Simple ID-Based Page

// app/[id]/page.tsx - Top-level dynamic route
interface PageProps {
  params: Promise<{ id: string }>;
}

export default async function ItemPage({ params }: PageProps) {
  const { id } = await params;

  const item = await fetch(`https://api.example.com/items/${id}`)
    .then(res => res.json());

  return (
    <div>
      <h1>{item.title}</h1>
      <p>{item.description}</p>
    </div>
  );
}

Pattern 2: Blog Post with Slug

// app/blog/[slug]/page.tsx
interface PageProps {
  params: Promise<{ slug: string }>;
}

export default async function BlogPost({ params }: PageProps) {
  const { slug } = await params;

  const post = await getPostBySlug(slug);

  return (
    <article>
      <h1>{post.title}</h1>
      <div dangerouslySetInnerHTML={{ __html: post.content }} />
    </article>
  );
}

// Generate static params for SSG
export async function generateStaticParams() {
  const posts = await getAllPosts();

  return posts.map((post) => ({
    slug: post.slug,
  }));
}

Pattern 3: Nested Resources

// app/users/[userId]/posts/[postId]/page.tsx
interface PageProps {
  params: Promise<{
    userId: string;
    postId: string;
  }>;
}

export default async function UserPost({ params }: PageProps) {
  const { userId, postId } = await params;

  const [user, post] = await Promise.all([
    getUserById(userId),
    getPostById(postId),
  ]);

  return (
    <div>
      <h1>{post.title}</h1>
      <p>By {user.name}</p>
      <div>{post.content}</div>
    </div>
  );
}

Pattern 4: Catch-All Routes

// app/docs/[...slug]/page.tsx - Matches /docs/a, /docs/a/b, /docs/a/b/c
interface PageProps {
  params: Promise<{
    slug: string[];  // Array of path segments
  }>;
}

export default async function DocsPage({ params }: PageProps) {
  const { slug } = await params;
  const path = slug.join('/');

  const doc = await getDocByPath(path);

  return <div>{doc.content}</div>;
}

// app/shop/[[...slug]]/page.tsx - Optional catch-all
// Matches /shop, /shop/electronics, /shop/electronics/phones
interface PageProps {
  params: Promise<{
    slug?: string[];  // Optional array
  }>;
}

export default async function ShopPage({ params }: PageProps) {
  const { slug = [] } = await params;

  if (slug.length === 0) {
    return <ShopHomepage />;
  }

  return <CategoryPage category={slug.join('/')} />;
}

TypeScript Best Practices

Type Safety for Params

// Define params type separately for reusability
type ProductPageParams = { id: string };

interface ProductPageProps {
  params: Promise<ProductPageParams>;
}

export default async function ProductPage({ params }: ProductPageProps) {
  const { id } = await params;
  // id is typed as string
}

// Reuse in generateMetadata
export async function generateMetadata({ params }: ProductPageProps) {
  const { id } = await params;
  const product = await getProduct(id);
  return { title: product.name };
}

Multiple Dynamic Segments

type PostPageParams = {
  category: string;
  slug: string;
};

interface PostPageProps {
  params: Promise<PostPageParams>;
  searchParams: Promise<{ [key: string]: string | string[] | undefined }>;
}

export default async function PostPage({ params, searchParams }: PostPageProps) {
  const { category, slug } = await params;
  const { view } = await searchParams;

  // All properly typed
}

Common Pitfalls and Solutions

Pitfall 1: Forgetting params is a Promise (Next.js 15+)

// ❌ WRONG
export default async function Page({ params }: { params: { id: string } }) {
  const product = await getProduct(params.id);  // Error: params is Promise
}

// ✅ CORRECT
export default async function Page({ params }: { params: Promise<{ id: string }> }) {
  const { id } = await params;
  const product = await getProduct(id);
}

Pitfall 2: Using params in Client Components without useParams

// ❌ WRONG - params prop doesn't exist in Client Components
'use client';

export default function ClientPage({ params }) {  // undefined!
  return <div>{params.id}</div>;
}

// ✅ CORRECT
'use client';
import { useParams } from 'next/navigation';

export default function ClientPage() {
  const params = useParams<{ id: string }>();
  return <div>{params.id}</div>;
}

Pitfall 3: Over-nesting Routes

// ❌ UNNECESSARY NESTING
// app/products/product/[id]/page.tsx
// URL: /products/product/123

// ✅ SIMPLER
// app/products/[id]/page.tsx
// URL: /products/123

// OR even simpler if product is the main resource:
// app/[id]/page.tsx
// URL: /123

Pitfall 4: Not Handling Invalid IDs

// ✅ ROBUST
export default async function ProductPage({
  params,
}: {
  params: Promise<{ id: string }>;
}) {
  const { id } = await params;

  const product = await fetch(`https://api.example.com/products/${id}`)
    .then(res => {
      if (!res.ok) throw new Error('Product not found');
      return res.json();
    });

  if (!product) {
    notFound();  // Shows 404 page
  }

  return <div>{product.name}</div>;
}

Decision Guide

When you need to create a dynamic route, ask:

1. What's the URL structure?

   • Single ID: [id]
   • Category + ID: category/[id]
   • Hierarchical: [category]/[id]
   • Flexible paths: [...slug]

2. Is this a Server or Client Component?

   • Server: Use params prop (await it in Next.js 15+)
   • Client: Use useParams() hook

3. Do I need the simplest structure?

   • When in doubt, use fewer nesting levels
   • Top-level routes are simpler and more direct

4. Am I on Next.js 15+?

   • Yes: params is Promise<{...}>
   • No: params is {...}

Examples: Real-World Scenarios

E-commerce Product Page

// app/products/[id]/page.tsx
import { notFound } from 'next/navigation';

interface Product {
  id: string;
  name: string;
  price: number;
  description: string;
}

async function getProduct(id: string): Promise<Product | null> {
  const res = await fetch(`https://api.example.com/products/${id}`, {
    next: { revalidate: 60 },  // Revalidate every 60s
  });

  if (!res.ok) return null;
  return res.json();
}

export default async function ProductPage({
  params,
}: {
  params: Promise<{ id: string }>;
}) {
  const { id } = await params;
  const product = await getProduct(id);

  if (!product) {
    notFound();
  }

  return (
    <div>
      <h1>{product.name}</h1>
      <p>${product.price}</p>
      <p>{product.description}</p>
    </div>
  );
}

export async function generateMetadata({
  params,
}: {
  params: Promise<{ id: string }>;
}) {
  const { id } = await params;
  const product = await getProduct(id);

  return {
    title: product?.name ?? 'Product Not Found',
    description: product?.description,
  };
}

Documentation Site with Nested Paths

// app/docs/[...slug]/page.tsx
interface DocPageProps {
  params: Promise<{ slug: string[] }>;
}

export default async function DocPage({ params }: DocPageProps) {
  const { slug } = await params;
  const path = slug.join('/');

  const doc = await getDocByPath(path);

  if (!doc) {
    notFound();
  }

  return (
    <article className="prose">
      <h1>{doc.title}</h1>
      <div dangerouslySetInnerHTML={{ __html: doc.html }} />
    </article>
  );
}

export async function generateStaticParams() {
  const docs = await getAllDocs();

  return docs.map((doc) => ({
    slug: doc.path.split('/'),
  }));
}

Checklist for Dynamic Routes

Before implementing a dynamic route, verify:

• Route structure is as simple as possible (default to top-level unless told otherwise)
• Not inferring route nesting from resource type names
• Route structure matches URL requirements (not over-nested)
• params is typed as Promise<{...}> for Next.js 15+
• params is awaited before accessing properties (Next.js 15+)
• Error handling for invalid IDs/slugs (use notFound())
• TypeScript types are properly defined
• Using Server Component unless client interactivity needed
• Consider generateStaticParams() for SSG if applicable
• Metadata generation if SEO matters

Quick Reference

Remember: Dynamic routes in Next.js are file-system based. The folder structure with [brackets] creates the dynamic segments, and the params prop (or useParams() hook) provides access to those values.

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