Dynamic Routing
All Next.js topics∙ Next.js
Dynamic routes use bracketed folder names such as [slug] to match variable URL segments. This lesson explains how it works, when to use it, how to implement it safely, and how to verify the result.
Syntax
app/posts/[slug]/page.tsxExample
// Topic: Dynamic Routing
import { notFound } from 'next/navigation';
export default async function PostPage({ params }) {
const { slug } = await params;
const post = await getPost(slug);
if (!post) notFound();
return <h1>{post.title}</h1>;
}Expected Output
The URL slug selects the matching post.Line-by-line
| Line | Meaning |
|---|---|
import { notFound } from 'next/navigation'; | Imports a component or framework API used by the example. |
export default async function PostPage({ params }) { | Exports the React component that Next.js renders for the route. |
const { slug } = await params; | Reads the resolved dynamic route parameters. |
const post = await getPost(slug); | Stores a value used later in the example. |
if (!post) notFound(); | Stops rendering and displays the nearest not-found UI. |
return <h1>{post.title}</h1>; | Returns the response or interface produced by the function. |
} | Forms part of the component, server operation, or configuration shown above. |
Real-World Uses
- 1Dynamic Routing is useful for building multi-page applications with stable URLs, shared layouts, and deep links.
- 2For /posts/hello, a route at app/posts/[slug]/page.tsx receives hello as the slug parameter.
- 3A team should use it when the requirement matches its responsibility in routing.
- 4It should fit the surrounding route, data, security, and deployment design instead of being added in isolation.
- 5A successful implementation is visible through correct URLs, predictable layouts, and navigation without full-page reloads.
Common Mistakes
- 1Assuming every parameter maps to valid data can produce broken pages or expose records without proper authorization.
- 2Copying an example without identifying which code runs on the server and which code reaches the browser.
- 3Handling only the happy path and forgetting loading, empty, invalid, unauthorized, and failed states.
- 4Adding client state or third-party libraries before confirming that built-in Next.js and browser features are insufficient.
- 5Skipping verification in a production build, where caching and runtime behavior can differ from development.
Best Practices
- 1Validate route parameters, fetch the matching record on the server, and call notFound() when no resource exists.
- 2Keep the owning route, component, server function, and validation responsibility easy to identify.
- 3Use server-side code for trusted data and secrets; send only the data required by interactive browser components.
- 4Make loading, empty, success, and error states explicit for the user.
- 5Test a valid value, an unknown value, encoded characters, direct refresh, generated static parameters, and permission checks.
What it means
- 1Dynamic routes use bracketed folder names such as [slug] to match variable URL segments.
- 2The important question is not only what syntax to write, but what responsibility this feature owns.
- 3Its behavior should be understood in development, during a production build, and after deployment.
- 4Before implementing it, decide what input it receives, what result it produces, and how failure is shown.
How it works
- 1For /posts/hello, a route at app/posts/[slug]/page.tsx receives hello as the slug parameter.
- 2Next.js uses file and component boundaries to decide routing, server execution, browser execution, and caching.
- 3Data should cross each boundary in a small, serializable, and validated form.
- 4The final result should remain understandable when a user refreshes the page or opens the URL directly.
Step-by-step approach
- 1Create the smallest route or component that demonstrates Dynamic Routing.
- 2Add one realistic input or data source and show the successful result.
- 3Add the most likely failure case and display a useful response.
- 4Run this check: Test a valid value, an unknown value, encoded characters, direct refresh, generated static parameters, and permission checks.
Production checklist
- 1Confirm server-only values and secrets never enter the browser bundle.
- 2Confirm direct URLs, refreshes, loading states, and errors behave correctly.
- 3Confirm caching and revalidation match the required data freshness.
- 4Measure the result using correct URLs, predictable layouts, and navigation without full-page reloads.
Quick Summary
- Dynamic routes use bracketed folder names such as [slug] to match variable URL segments.
- For /posts/hello, a route at app/posts/[slug]/page.tsx receives hello as the slug parameter.
- Recommended approach: Validate route parameters, fetch the matching record on the server, and call notFound() when no resource exists.
- Main mistake to avoid: Assuming every parameter maps to valid data can produce broken pages or expose records without proper authorization.
- Verify it by doing the following: Test a valid value, an unknown value, encoded characters, direct refresh, generated static parameters, and permission checks.
Interview Questions
Q1. What is Dynamic Routing?
Answer: Dynamic routes use bracketed folder names such as [slug] to match variable URL segments.
Q2. How does Dynamic Routing work in Next.js?
Answer: For /posts/hello, a route at app/posts/[slug]/page.tsx receives hello as the slug parameter.
Q3. When should you use Dynamic Routing?
Answer: Use it for building multi-page applications with stable URLs, shared layouts, and deep links, when that responsibility belongs inside the Next.js application.
Q4. What is a common mistake with Dynamic Routing?
Answer: Assuming every parameter maps to valid data can produce broken pages or expose records without proper authorization.
Q5. How would you test Dynamic Routing?
Answer: Test a valid value, an unknown value, encoded characters, direct refresh, generated static parameters, and permission checks. The result should demonstrate correct URLs, predictable layouts, and navigation without full-page reloads.
Quiz
Which approach is best when implementing Dynamic Routing?