Route parameters in React

Introduction

Route parameters let your app get information from the URL. This helps show different content based on what the user clicks or types.

Showing a user profile page based on the user ID in the URL.

Displaying details of a product when clicking on it in a list.

Navigating to a blog post page using the post's unique ID.

Filtering content by category or tag from the URL.

Creating dynamic pages where the content changes with the URL.

Syntax

React

import { useParams } from 'react-router-dom';

function Component() {
  const params = useParams();
  // Access params.id or other keys
  return <div>{params.id}</div>;
}

useParams is a React hook from react-router-dom that reads parameters from the URL.

Route parameters are defined in the route path with a colon, like /user/:id.

Examples

This example gets the id parameter from the URL and shows it.

React

import { useParams } from 'react-router-dom';

function User() {
  const { id } = useParams();
  return <h1>User ID: {id}</h1>;
}

Here, the route expects a productId parameter to display product details.

React

import { useParams } from 'react-router-dom';

function Product() {
  const { productId } = useParams();
  return <p>Product number: {productId}</p>;
}

You can also get all parameters as an object and access them by name.

React

import { useParams } from 'react-router-dom';

function Post() {
  const params = useParams();
  return <div>Post slug: {params.slug}</div>;
}

Sample Program

This app has a home page with links to two user profiles. Clicking a link changes the URL with a user ID. The UserProfile component reads that ID from the URL and shows it.

React

import React from 'react';
import { BrowserRouter as Router, Routes, Route, Link, useParams } from 'react-router-dom';

function UserProfile() {
  const { userId } = useParams();
  return <h2>User Profile for ID: {userId}</h2>;
}

function Home() {
  return (
    <div>
      <h1>Home</h1>
      <nav>
        <ul>
          <li><Link to="/user/101">User 101</Link></li>
          <li><Link to="/user/202">User 202</Link></li>
        </ul>
      </nav>
    </div>
  );
}

export default function App() {
  return (
    <Router>
      <Routes>
        <Route path="/" element={<Home />} />
        <Route path="/user/:userId" element={<UserProfile />} />
      </Routes>
    </Router>
  );
}

Important Notes

Route parameters are always strings. Convert them if you need numbers.

If a parameter is missing, useParams() returns undefined for it.

Use semantic HTML and accessible links for better user experience.

Summary

Route parameters let your app read values from the URL to show dynamic content.

Use useParams() hook inside components to get these values.

Define parameters in route paths with a colon, like /user/:id.

Practice

1. What does the useParams() hook in React Router do?

easy

A. It sets new route paths dynamically.

B. It retrieves the dynamic parameters from the current URL.

C. It navigates to a different route programmatically.

D. It renders a list of all available routes.

Solution

1. Step 1: Understand the purpose of useParams()

   This hook is designed to extract parameters defined in the route path from the URL.

2. Step 2: Compare with other options

   Options A, C, and D describe different React Router features, not useParams().

3. Final Answer:

   It retrieves the dynamic parameters from the current URL. -> Option B

4. Quick Check:

   useParams() = get URL parameters [OK]

Hint: Remember: useParams() reads URL values, not changes routes. [OK]

Common Mistakes:

• Confusing useParams() with navigation functions like useNavigate()
• Thinking useParams() sets or changes routes
• Assuming useParams() returns all routes instead of parameters

2. Which of the following is the correct way to define a route with a parameter named postId in React Router?

easy

A. <Route path="/post/:postId" element={<Post />} />

B. <Route path="/post/*postId" element={<Post />} />

C. <Route path="/post/postId" element={<Post />} />

D. <Route path="/post/{postId}" element={<Post />} />

Solution

1. Step 1: Identify parameter syntax in route paths

   React Router uses a colon : before the parameter name to define dynamic segments.

2. Step 2: Check each option

   <Route path="/post/:postId" element={<Post />} /> correctly uses /:postId. Options A, B, and D use incorrect syntax.

3. Final Answer:

   <Route path="/post/:postId" element={<Post />} /> -> Option A

4. Quick Check:

   Parameter syntax = colon before name [OK]

Hint: Use colon before parameter name in route path. [OK]

Common Mistakes:

• Omitting the colon before parameter name
• Using curly braces or asterisk instead of colon
• Confusing parameter syntax with query strings

3. Given the route <Route path="/profile/:username" element={<Profile />} /> and the URL /profile/jane_doe, what will useParams() return inside the Profile component?

medium

A. {"username": ":jane_doe"}

B. {"profile": "jane_doe"}

C. {"username": "jane_doe"}

D. {} (empty object)

Solution

1. Step 1: Match URL segment to route parameter

   The route defines :username as a parameter. The URL /profile/jane_doe assigns "jane_doe" to this parameter.

2. Step 2: Understand useParams() output

   useParams() returns an object with keys as parameter names and values as the matched URL parts.

3. Final Answer:

   {"username": "jane_doe"} -> Option C

4. Quick Check:

   useParams() returns {paramName: value} [OK]

Hint: useParams() keys match route parameters exactly. [OK]

Common Mistakes:

• Including colon in parameter value
• Using wrong parameter name as key
• Expecting empty object when parameter exists

4. Consider this code snippet inside a React Router app:

const params = useParams();
console.log(params.id);

But the route is defined as <Route path="/product/:productId" element={<Product />} />. What is the problem?

medium

A. The parameter name used in useParams() does not match the route parameter name.

B. useParams() cannot be used inside functional components.

C. The route path should not have a colon before the parameter name.

D. The element prop must be a string, not a component.

Solution

1. Step 1: Compare parameter names in route and code

   The route defines parameter as productId, but code accesses params.id.

2. Step 2: Understand useParams() object keys

   useParams() keys exactly match route parameter names, so params.id is undefined here.

3. Final Answer:

   The parameter name used in useParams() does not match the route parameter name. -> Option A

4. Quick Check:

   Param names must match exactly [OK]

Hint: Check parameter names match exactly in route and useParams(). [OK]

Common Mistakes:

• Assuming useParams() keys are generic like 'id'
• Thinking useParams() works outside components
• Misunderstanding route parameter syntax

5. You want to create a route that shows a user's post by user ID and post ID, like /user/42/post/7. Which route path and useParams() usage correctly extract both parameters inside the component?

hard

A. <Route path="/user/:userId/post/:postId" element={<UserPost />} />Inside component: const [userId, postId] = useParams();

B. <Route path="/user/:userId/post/:postId" element={<UserPost />} />Inside component: const params = useParams(); const user = params.user; const post = params.post;

C. <Route path="/user/:userId/post/:postId" element={<UserPost />} />Inside component: const { id1, id2 } = useParams();

D. <Route path="/user/:userId/post/:postId" element={<UserPost />} />Inside component: const { userId, postId } = useParams();

Solution

1. Step 1: Define route with multiple parameters

   The route path correctly uses :userId and :postId to capture both values.

2. Step 2: Correctly extract parameters inside component

   useParams() returns an object, so destructuring with matching keys { userId, postId } is correct. Options A, B, and C misuse keys or destructuring.

3. Final Answer:

   <Route path="/user/:userId/post/:postId" element={<UserPost />} /> with const { userId, postId } = useParams(); -> Option D

4. Quick Check:

   Multiple params = multiple keys in useParams() object [OK]

Hint: Destructure useParams() with exact route parameter names. [OK]

Common Mistakes:

• Using wrong keys when destructuring useParams()
• Trying to destructure useParams() as an array
• Accessing non-existent keys from useParams()