Route parameters in React - Mini Project: Build & Apply

React Route Parameters

📖 Scenario: You are building a simple React app that shows user profiles based on the URL.Each user has a unique ID in the URL, and the app should read this ID to display the correct profile.

🎯 Goal: Create a React app using React Router that reads a userId from the URL and displays it on the page.

📋 What You'll Learn

Use React Router to define routes

Create a route with a parameter named userId

Create a functional component that reads the userId parameter

Display the userId inside the component

💡 Why This Matters

🌍 Real World

Many web apps show different content based on URL parts, like user profiles or product pages. Route parameters let apps read these parts easily.

💼 Career

Understanding route parameters is essential for frontend developers working with React Router to build dynamic, user-friendly web apps.

1

Set up the basic React Router structure

Create a React component called App that uses BrowserRouter and Routes from react-router-dom. Inside Routes, add a route with path /user/:userId and element <UserProfile />. Also create a placeholder UserProfile component that returns an empty fragment <></>.

React

import React from 'react';
import { BrowserRouter, Routes, Route } from 'react-router-dom';

function UserProfile() {
  // Your code here
}

function App() {
  return (
    
      
        {/* Your code here */}
      
    
  );
}

export default App

Hint

Remember to import BrowserRouter, Routes, and Route from react-router-dom.

Define the route path exactly as /user/:userId.

2

Add a hook to read the route parameter

Inside the UserProfile component, import and use the useParams hook from react-router-dom. Create a constant called params by calling useParams().

React

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

function UserProfile() {
  const params = useParams();
  // Your code here
}

function App() {
  return (
    
      
        } />
      
    
  );
}

export default App

Hint

Import useParams from react-router-dom and call it inside UserProfile.

3

Display the userId parameter in the component

Inside the UserProfile component, return a <div> that shows the text User ID: followed by the value of params.userId.

React

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

function UserProfile() {
  const params = useParams();
  // Your code here
}

function App() {
  return (
    
      
        } />
      
    
  );
}

export default App

Hint

Use curly braces {} inside JSX to insert the value of params.userId.

4

Add a link to test the route parameter

In the App component, above Routes, add a <nav> element containing a <a> tag with href "/user/42" and text Go to User 42.

React

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

function UserProfile() {
  const params = useParams();
  return User ID: {params.userId};
}

function App() {
  return (
    
      {/* Your code here */}
      
        } />
      
    
  );
}

export default App

Hint

Add a navigation link so you can click and test the route parameter in the browser.

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()