Dynamic route parameters in Remix

Introduction

Dynamic route parameters let your app show different pages based on parts of the URL. This helps create pages for many items without making a file for each one.

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

Displaying a blog post page using the post's unique slug from the URL.

Creating product detail pages where the product ID changes in the URL.

Building category pages where the category name is part of the URL.

Syntax

Remix

app/routes/$paramName.tsx

The $paramName part in the filename tells Remix this is a dynamic segment.

You can access the parameter inside your component using the useParams() hook.

Examples

This example shows a dynamic route for user profiles. The URL /123 will show User ID: 123.

Remix

app/routes/$userId.tsx

import { useParams } from '@remix-run/react';

export default function UserProfile() {
  const params = useParams();
  return <div>User ID: {params.userId}</div>;
}

This example uses a dynamic slug for blog posts. The URL /blog/my-first-post will show Blog post: my-first-post.

Remix

app/routes/blog/$slug.tsx

import { useParams } from '@remix-run/react';

export default function BlogPost() {
  const { slug } = useParams();
  return <h1>Blog post: {slug}</h1>;
}

Sample Program

This component shows product details based on the product ID from the URL. For example, visiting /42 will display the product ID 42.

Remix

app/routes/$productId.tsx

import { useParams } from '@remix-run/react';

export default function ProductPage() {
  const { productId } = useParams();
  return (
    <main>
      <h1>Product Details</h1>
      <p>Product ID: {productId}</p>
    </main>
  );
}

Important Notes

Dynamic route files must start with $ to tell Remix they are dynamic.

You can have multiple dynamic parameters by nesting folders or using multiple $param files.

Remember to use useParams() inside your component to get the current URL values.

Summary

Dynamic route parameters let you create flexible pages that change based on the URL.

Use $paramName in filenames and useParams() in components to access them.

This helps build apps with many similar pages without making many files.

Practice

1. What does a dynamic route parameter in Remix allow you to do?

easy

A. Create pages that change content based on the URL

B. Make the app load faster by caching pages

C. Automatically style pages with CSS

D. Prevent users from accessing certain pages

Solution

1. Step 1: Understand dynamic routes

   Dynamic routes let pages show different content depending on URL parts.

2. Step 2: Identify the purpose

   This means one page file can handle many URLs by reading parameters.

3. Final Answer:

   Create pages that change content based on the URL -> Option A

4. Quick Check:

   Dynamic routes = flexible pages [OK]

Hint: Dynamic routes change page content by URL parts [OK]

Common Mistakes:

• Thinking dynamic routes speed up loading
• Confusing dynamic routes with styling
• Believing dynamic routes block access

2. Which filename correctly defines a dynamic route parameter for a user ID in Remix?

easy

A. user.$id.jsx

B. userId$.jsx

C. $userId.jsx

D. user.$userId.jsx

Solution

1. Step 1: Recall Remix dynamic route syntax

   Dynamic parameters use a $ prefix in the filename, like $paramName.jsx.

2. Step 2: Match correct filename

   For user ID, $userId.jsx is correct; others have extra dots or misplaced $.

3. Final Answer:

   $userId.jsx -> Option C

4. Quick Check:

   Dynamic param filename = $paramName.jsx [OK]

Hint: Use $ before param name in filename for dynamic routes [OK]

Common Mistakes:

• Putting $ after the dot in filename
• Using multiple $ signs
• Naming file without $ for dynamic param

3. Given this Remix route file routes/$postId.jsx with code:

import { useParams } from '@remix-run/react';
export default function Post() {
  const params = useParams();
  return <div>Post ID: {params.postId}</div>;
}

What will be rendered when visiting URL /123?

medium

A. Post ID: postId

B. Post ID: 123

C. Post ID: undefined

D. Error: useParams not found

Solution

1. Step 1: Understand useParams behavior

   useParams() returns an object with keys matching dynamic route names and values from URL.

2. Step 2: Match URL to param

   URL /123 sets postId to '123', so params.postId is '123'.

3. Final Answer:

   Post ID: 123 -> Option B

4. Quick Check:

   useParams() returns URL param values [OK]

Hint: useParams() keys match $param names in filename [OK]

Common Mistakes:

• Expecting param name as string instead of value
• Forgetting to import useParams
• Assuming useParams returns undefined

4. What is wrong with this Remix route file named routes/$user.jsx? It contains:

import { useParams } from '@remix-run/react';
export default function User() {
  const { userId } = useParams();
  return <div>User: {userId}</div>;
}

medium

A. The filename parameter and useParams key do not match

B. useParams cannot be destructured

C. JSX must use parentheses around return

D. Dynamic route files cannot be named with $

Solution

1. Step 1: Check filename parameter name

   Filename uses $user.jsx, so param name is 'user'.

2. Step 2: Check useParams destructuring

   Code destructures 'userId' which does not exist in params; should use 'user'.

3. Final Answer:

   The filename parameter and useParams key do not match -> Option A

4. Quick Check:

   Param name in filename = key in useParams [OK]

Hint: Param name in filename and useParams must match exactly [OK]

Common Mistakes:

• Destructuring wrong param name
• Thinking useParams can't be destructured
• Believing $ in filename is invalid

5. You want to create a Remix route that shows a product page with a dynamic productId and also fetches product data server-side. Which filename and code snippet correctly use dynamic route parameters and server loader?

hard

A. routes/$productId.jsx withimport { useLoaderData, useParams } from '@remix-run/react';
export async function loader({ params }) {
return fetch(`https://api.example.com/products/${params.id}`);
}
export default function Product() {
const product = useLoaderData();
const { productId } = useParams();
return <div>Product {productId}: {product.name}</div>;
}

B. routes/product.$id.jsx withexport async function loader({ params }) {
return fetch(`https://api.example.com/products/${params.id}`);
}
export default function Product() {
const product = useLoaderData();
return <div>Product: {product.name}</div>;
}

C. routes/$productId.jsx withexport async function loader() {
return fetch('https://api.example.com/products');
}
export default function Product() {
const product = useLoaderData();
return <div>Product: {product.name}</div>;
}

D. routes/$productId.jsx withimport { useLoaderData } from '@remix-run/react';
export async function loader({ params }) {
return fetch(`https://api.example.com/products/${params.productId}`);
}
export default function Product() {
const product = useLoaderData();
return <div>Product: {product.id}</div>;
}

Solution

1. Step 1: Check filename for dynamic param

   Filename $productId.jsx correctly defines dynamic param 'productId'.

2. Step 2: Verify loader and component

   Loader uses params.productId to fetch product data, matching filename param. Component uses useLoaderData() and renders correctly.

3. Final Answer:

   routes/$productId.jsx with loader using params.productId -> Option D

4. Quick Check:

   Filename param = params key = loader fetch param [OK]

Hint: Match filename param, loader params, and useLoaderData usage [OK]

Common Mistakes:

• Mismatching param names in filename and loader
• Not using params in loader
• Ignoring useLoaderData for fetched data