Upgrading Docusaurus from 3.1.0 to 3.9.2 | Node.js 20 Migration Guide

Maintaining documentation is a long-term commitment. As frameworks evolve, upgrades become inevitable to stay secure, supported, and compatible with modern tooling. This blog documents a real-world upgrade journey from Docusaurus 3.1.0 to Docusaurus 3.9.2, along with a Node.js upgrade to version 20, and the MDX and Markdown fixes required to get the project building successfully again.

The goal of this guide is to help teams avoid common pitfalls and understand why certain issues appear during the upgrade.

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Why Upgrade Docusaurus and Node.js

Docusaurus Upgrade Motivation

Upgrading from Docusaurus 3.1.0 to 3.9.2 provides:

• Improved MDX parsing and validation
• Better ESM and Vite compatibility
• Security fixes and dependency updates
• More predictable theme and plugin behavior

Node.js 20 Requirement

Docusaurus 3.9.2 officially supports modern Node.js versions. Node.js 16 is deprecated, and Node.js 18 is approaching maintenance mode. Upgrading to Node.js 20 ensures:

• Long-term support
• Faster builds
• Better compatibility with modern tooling

For teams deploying documentation alongside applications on Nife’s platform, aligning Node.js versions avoids runtime inconsistencies.

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Step 1: Upgrade Node.js to Version 20

Before touching Docusaurus, ensure Node.js is upgraded.

Using NVM:

Copynvm install 20
nvm use 20
node -v

Verify npm as well:

Copynpm -v

Clean the environment:

Copyrm -rf node_modules package-lock.json
npm cache clean --force

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Step 2: Upgrade Docusaurus to 3.9.2

Update all Docusaurus-related dependencies together to avoid version mismatches.

Copynpm install @docusaurus/core@3.9.2 \
            @docusaurus/preset-classic@3.9.2

If you are using additional plugins or themes, upgrade them to matching versions.

After installation:

Copynpm install
npm run build

At this stage, most projects will fail due to MDX or theme-related issues.

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Step 3: Common MDX and Markdown Breaking Changes

1. Stricter MDX Parsing

Docusaurus 3.9.2 enforces stricter MDX rules.

Common Issues

• Unclosed JSX tags
• Invalid HTML inside Markdown
• Incorrect frontmatter formatting
• Trailing commas in arrays

Example Fix

Incorrect:

Copy<img src="./img/sample.png">

Correct:

Copy<img src="./img/sample.png" />

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2. Frontmatter Validation Errors

Ensure all frontmatter fields are valid YAML.

Incorrect:

Copykeywords: [docs, guide, ]

Correct:

Copykeywords: [docs, guide]

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3. JSX Must Be Explicit in MDX

Any JSX expression must be properly wrapped.

Incorrect:

Copy{someFunction()}

Correct:

Copy{someFunction && someFunction()}

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Step 4: Fixing Image Imports in MDX

Docusaurus 3.x requires explicit image imports when using JSX.

Recommended pattern:

Copy<img
  src={require('./img/architecture.png').default}
  alt="Architecture Diagram"
  width="800"
/>

Avoid relative Markdown image syntax for complex layouts.

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Step 5: Theme Component Errors After Upgrade

One of the most common errors during upgrade:

CopyModule not found: Error: Can't resolve '@theme/Hero'

Why This Happens

• Docusaurus 3.9.2 removed or refactored internal theme components
• Custom themes built for older versions are incompatible

Resolution Strategy

1. Temporarily disable all custom theme components
2. Replace theme imports with standard MDX or React components
3. Gradually reintroduce custom components after validation

Example removal:

Copy// Remove this
import Hero from '@theme/Hero';

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Step 6: Sidebar and Routing Validation

Docusaurus 3.9.2 enforces stricter route validation.

Ensure:

• All sidebar paths exist
• Slugs are unique
• No duplicate document IDs

Run:

Copynpm run clear
npm run build

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Step 7: Final Build and Verification

Once MDX and theme issues are resolved:

Copynpm run build
npm run serve

Verify:

• All pages load correctly
• Sidebar navigation works
• Images render as expected
• No console warnings or errors

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Key Takeaways

• Always upgrade Node.js before upgrading Docusaurus
• Expect MDX parsing to be stricter in newer versions
• Custom themes are the most common breaking point
• Clean installs prevent dependency conflicts
• Incremental fixes are faster than mass refactors

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Conclusion

Upgrading from Docusaurus 3.1.0 to 3.9.2 with Node.js 20 is not just a dependency bump. It is a validation of documentation quality, MDX correctness, and long-term maintainability**Nife containerized deployments**.

By addressing MDX issues early and removing outdated theme dependencies, teams can ensure a smooth and future-proof documentation platform.

This upgrade prepares your documentation for scalability, security, and continued evolution alongside your product**Nife**.