GenerateMetadata for dynamic metadata in NextJS

Introduction

GenerateMetadata lets you create page titles and descriptions that change based on the page content. This helps your website show the right info in search results and browser tabs.

You want each blog post to have its own title and description.

You have a product page that shows different product names and details.

You want to update metadata based on user input or URL parameters.

You want better SEO by customizing metadata for each page dynamically.

Syntax

NextJS

export async function generateMetadata({ params }) {
  // fetch or compute data based on params
  return {
    title: `Title for ${params.id}`,
    description: `Description for ${params.id}`
  };
}

The function must be async if you fetch data.

Return an object with metadata fields like title and description.

Examples

Static metadata without parameters.

NextJS

export async function generateMetadata() {
  return {
    title: 'Home Page',
    description: 'Welcome to the home page'
  };
}

Dynamic metadata using URL parameters.

NextJS

export async function generateMetadata({ params }) {
  return {
    title: `Post: ${params.slug}`,
    description: `Read about ${params.slug}`
  };
}

Fetching data to create metadata dynamically.

NextJS

export async function generateMetadata({ params }) {
  const data = await fetch(`https://api.example.com/posts/${params.slug}`);
  const post = await data.json();
  return {
    title: post.title,
    description: post.summary
  };
}

Sample Program

This example shows a page component that uses generateMetadata to set the page title and description based on the URL parameter slug. The page content also uses the slug to display the post.

NextJS

import React from 'react';

export async function generateMetadata({ params }) {
  const post = {
    title: `Post about ${params.slug}`,
    description: `This is a detailed post about ${params.slug}.`
  };
  return post;
}

export default function PostPage({ params }) {
  return (
    <main>
      <h1>{`Post: ${params.slug}`}</h1>
      <p>{`Content for post ${params.slug} goes here.`}</p>
    </main>
  );
}

Important Notes

Always return an object with metadata fields from generateMetadata.

Use params to access dynamic route parts.

Metadata updates help search engines and improve user experience.

Summary

GenerateMetadata creates dynamic page titles and descriptions.

It runs on the server before the page renders.

Use it to improve SEO and show relevant info per page.

Practice

1. What is the main purpose of the generateMetadata function in Next.js?

easy

A. To fetch data on the client after page load

B. To handle client-side routing between pages

C. To create dynamic page titles and descriptions before rendering

D. To style components dynamically using CSS

Solution

1. Step 1: Understand the role of generateMetadata

   This function runs on the server before the page renders to set metadata dynamically.

2. Step 2: Identify its main use

   It is used to create dynamic page titles and descriptions for SEO and relevant info.

3. Final Answer:

   To create dynamic page titles and descriptions before rendering -> Option C

4. Quick Check:

   Dynamic metadata = To create dynamic page titles and descriptions before rendering [OK]

Hint: Remember: generateMetadata sets SEO info before page loads [OK]

Common Mistakes:

• Confusing generateMetadata with client-side data fetching
• Thinking it handles routing or styling
• Assuming it runs on the client

2. Which of the following is the correct syntax to export a generateMetadata function in a Next.js page?

easy

A. export const generateMetadata = () => { document.title = 'Page' }

B. export async function generateMetadata() { return { title: 'Page' } }

C. function generateMetadata() { console.log('metadata') } export generateMetadata

D. export default function generateMetadata() { return Page }

Solution

1. Step 1: Recall correct export syntax

   Next.js expects generateMetadata as an exported async function returning an object with metadata.

2. Step 2: Check each option

   export async function generateMetadata() { return { title: 'Page' } } correctly exports an async function returning an object with a title property.

3. Final Answer:

   export async function generateMetadata() { return { title: 'Page' } } -> Option B

4. Quick Check:

   Correct export syntax = export async function generateMetadata() { return { title: 'Page' } } [OK]

Hint: Use async function returning object for generateMetadata [OK]

Common Mistakes:

• Using default export instead of named export
• Returning JSX instead of an object
• Trying to set document.title inside generateMetadata

3. Given this generateMetadata function, what will be the page title?

export async function generateMetadata({ params }) {
  return { title: `User: ${params.username}` };
}

And the URL is /user/jane.

medium

A. User: jane

B. User: params.username

C. User: undefined

D. User: /user/jane

Solution

1. Step 1: Understand parameter usage

   The function receives params with username from the URL segment.

2. Step 2: Substitute params.username with actual value

   Since URL is /user/jane, params.username is 'jane', so title becomes 'User: jane'.

3. Final Answer:

   User: jane -> Option A

4. Quick Check:

   Dynamic title uses params.username = User: jane [OK]

Hint: URL params fill template strings in generateMetadata [OK]

Common Mistakes:

• Using literal string 'params.username' instead of value
• Assuming params is undefined without route setup
• Confusing URL path with metadata title

4. What is wrong with this generateMetadata function?

export function generateMetadata() {
  return { title: 'Home' }
  console.log('Metadata generated')
}

medium

A. generateMetadata cannot be a named export

B. The function must be async to work

C. The return value must be a string, not an object

D. The console.log runs after return and is unreachable

Solution

1. Step 1: Analyze function flow

   The return statement ends the function immediately, so code after it won't run.

2. Step 2: Identify unreachable code

   The console.log after return is unreachable and will never execute.

3. Final Answer:

   The console.log runs after return and is unreachable -> Option D

4. Quick Check:

   Code after return is unreachable = The console.log runs after return and is unreachable [OK]

Hint: Code after return is ignored, place logs before return [OK]

Common Mistakes:

• Thinking function must be async always
• Expecting return to accept strings only
• Confusing export types

5. You want to create dynamic metadata for a blog post page that shows the post title and author. Which generateMetadata implementation correctly handles this using params and fetch to get post data asynchronously?

hard

A. export async function generateMetadata({ params }) {
const post = await fetch(`/api/posts/${params.id}`).then(res => res.json());
return { title: post.title, description: `By ${post.author}` };
}

B. export function generateMetadata({ params }) {
const post = fetch(`/api/posts/${params.id}`).then(res => res.json());
return { title: post.title, description: `By ${post.author}` };
}

C. export async function generateMetadata() {
const post = await fetch('/api/posts').then(res => res.json());
return { title: post.title, description: post.author };
}

D. export async function generateMetadata({ params }) {
return { title: params.title, description: params.author };
}

Solution

1. Step 1: Identify async data fetching

   To get post data dynamically, generateMetadata must be async and await the fetch call.

2. Step 2: Check usage of params and fetch

   export async function generateMetadata({ params }) { const post = await fetch(`/api/posts/${params.id}`).then(res => res.json()); return { title: post.title, description: `By ${post.author}` }; } correctly awaits fetch with params.id and returns metadata using fetched data.

3. Final Answer:

   export async function generateMetadata({ params }) { const post = await fetch(`/api/posts/${params.id}`).then(res => res.json()); return { title: post.title, description: `By ${post.author}` }; } -> Option A

4. Quick Check:

   Async fetch with params used correctly = export async function generateMetadata({ params }) { const post = await fetch(`/api/posts/${params.id}`).then(res => res.json()); return { title: post.title, description: `By ${post.author}` }; } [OK]

Hint: Use async/await with params to fetch dynamic metadata [OK]

Common Mistakes:

• Not awaiting fetch causing unresolved promises
• Ignoring params and fetching all posts
• Returning params directly without fetching data