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Fixing 'Type '{}' is not assignable to type 'ReactNode': Why FontAwesomeIcon JSX Error Occurs in Vercel but Not Locally

If you’ve ever built a React or Next.js application using Font Awesome icons, you might have encountered a perplexing scenario: your app runs flawlessly locally, but when deploying to Vercel, you’re hit with a TypeScript error like:

Type '{}' is not assignable to type 'ReactNode'.

This error typically points to a mismatch in how the FontAwesomeIcon component is typed or resolved during the build process. While local environments often overlook or suppress such issues, Vercel’s strict production build pipeline (which enforces TypeScript checks more rigorously) exposes them.

In this blog, we’ll demystify why this error occurs, explore the key differences between local and Vercel environments that trigger it, and provide actionable solutions to fix it for good.

2026-02

Table of Contents#

  1. Understanding the Error: What ‘Type ‘{}’ is not assignable to type ‘ReactNode’’ Means
  2. Why It Works Locally but Fails on Vercel: Key Environment Differences
  3. Common Causes of the FontAwesomeIcon JSX Error
  4. Step-by-Step Solutions to Fix the Error
  5. Testing the Fix Locally Before Deploying to Vercel
  6. Troubleshooting Persistent Errors
  7. Conclusion
  8. References

1. Understanding the Error: What ‘Type ‘{}’ is not assignable to type ‘ReactNode’’ Means#

Before diving into fixes, let’s decode the error message:

  • ReactNode: In React, ReactNode is a type that represents any valid value that can be rendered: elements, strings, numbers, null, undefined, or arrays of these. It’s the return type for components and JSX expressions.
  • Type '{}': An empty object ({}) is being returned where a ReactNode is expected. This usually happens when a component fails to resolve correctly (e.g., due to missing dependencies, incorrect imports, or bundling errors) and defaults to an empty object instead of a valid React component.

In the context of FontAwesomeIcon, this error suggests that TypeScript cannot recognize FontAwesomeIcon as a valid React component in the production build. Instead, it infers the type as {}, which conflicts with the expected ReactNode type for JSX elements.

2. Why It Works Locally but Fails on Vercel: Key Environment Differences#

Local development environments and Vercel’s production pipeline behave differently in ways that can mask or expose TypeScript errors:

Local EnvironmentVercel Production Environment
Uses tsconfig.json (often with strict: false).May use a stricter tsconfig.prod.json (with strict: true).
Dev dependencies (e.g., @types/*) are available.Production builds may omit dev dependencies (if not properly declared).
Looser bundling (e.g., webpack development mode skips tree-shaking).Aggressive tree-shaking and minification can remove "unused" code.
May use npm install (installs all deps), while Vercel uses npm ci (strictly follows package-lock.json).npm ci ensures exact dependency versions but can expose missing deps.

These differences mean issues like missing type definitions, incorrect imports, or outdated dependencies are often hidden locally but surface on Vercel.

3. Common Causes of the FontAwesomeIcon JSX Error#

Let’s break down the root causes of the Type '{}' error with FontAwesomeIcon:

Cause 1: Missing or Outdated Type Definitions#

Font Awesome's React component (@fortawesome/react-fontawesome) includes built-in TypeScript types. If:

  • The types are outdated (e.g., incompatible with your @fortawesome/react-fontawesome version), or
  • TypeScript is not properly configured to resolve them,

TypeScript will fail to recognize FontAwesomeIcon as a valid component, leading to the {} type inference.

Cause 2: Incorrect TypeScript Configuration#

Vercel may use a production-specific tsconfig.json (e.g., tsconfig.prod.json) with stricter settings like strict: true or moduleResolution: Node16. If your tsconfig lacks settings like esModuleInterop: true or has an incorrect jsx mode, TypeScript may misinterpret the FontAwesomeIcon module.

Cause 3: Wrong Import Statements#

A common mistake is importing FontAwesomeIcon from the wrong path or using a default import instead of a named import. For example:

// Incorrect  
import FontAwesomeIcon from '@fortawesome/react-fontawesome'; // Default import (doesn't exist!)  
 
// Correct  
import { FontAwesomeIcon } from '@fortawesome/react-fontawesome'; // Named import

Cause 4: React/TypeScript Version Conflicts#

If your @types/react version is incompatible with your React version (e.g., react@18 with @types/react@17), TypeScript may misalign ReactNode definitions, causing conflicts with FontAwesomeIcon.

Cause 5: Tree-Shaking of Unused Icons#

Vercel’s production builds (especially with Next.js or Vite) use tree-shaking to remove unused code. If icons are not explicitly imported or registered, bundlers may mistakenly exclude FontAwesomeIcon, leaving an empty object ({}) in its place.

4. Step-by-Step Solutions to Fix the Error#

Solution 1: Update Font Awesome Dependencies and Types#

First, ensure all Font Awesome packages and their types are up to date and correctly installed.

Step 1.1: Install/Update Core Dependencies#

Run these commands to install the latest versions of Font Awesome’s React component, core library, and a free icon pack (e.g., free-solid-svg-icons):

# Using npm  
npm install @fortawesome/react-fontawesome@latest @fortawesome/fontawesome-svg-core@latest @fortawesome/free-solid-svg-icons@latest  
 
# Using yarn  
yarn add @fortawesome/react-fontawesome@latest @fortawesome/fontawesome-svg-core@latest @fortawesome/free-solid-svg-icons@latest

Solution 2: Verify TypeScript Configuration#

Ensure your tsconfig.json (or tsconfig.prod.json for production) has settings that align with Font Awesome’s module structure.

Key tsconfig.json Settings to Check:#

{  
  "compilerOptions": {  
    "strict": true, // Enables strict type-checking (mimic Vercel's strictness locally)  
    "moduleResolution": "NodeNext", // Modern module resolution (works with ES modules)  
    "esModuleInterop": true, // Fixes default vs named import conflicts  
    "jsx": "react-jsx", // Required for React 17+ JSX transforms  
    "skipLibCheck": false // Do NOT skip type checks for library code (critical!)  
  }  
}
  • skipLibCheck: false: Disabling this ensures TypeScript checks library type definitions for validity.
  • moduleResolution: NodeNext: Ensures TypeScript correctly resolves ES modules (Font Awesome uses ES modules).

Solution 3: Correct Import Statements for FontAwesomeIcon#

Always use the named import for FontAwesomeIcon from @fortawesome/react-fontawesome. Here’s a correct example:

// Correct: Named import  
import { FontAwesomeIcon } from '@fortawesome/react-fontawesome';  
import { faCoffee } from '@fortawesome/free-solid-svg-icons';  
 
function MyComponent() {  
  return (  
    <div>  
      <FontAwesomeIcon icon={faCoffee} /> {/* Valid ReactNode */}  
    </div>  
  );  
}

Avoid these mistakes:

  • Default imports (e.g., import FontAwesomeIcon from '@fortawesome/react-fontawesome').
  • Importing from subpaths (e.g., @fortawesome/react-fontawesome/dist/index).

Solution 4: Resolve React and TypeScript Version Conflicts#

Ensure react, react-dom, and their types are compatible:

Step 4.1: Check Versions#

Run npm list react @types/react (or yarn list) to verify:

Step 4.2: Update Conflicting Packages#

If versions are mismatched, update them:

# Using npm  
npm install react@latest react-dom@latest @types/react@latest @types/react-dom@latest  
 
# Using yarn  
yarn add react@latest react-dom@latest @types/react@latest @types/react-dom@latest

Solution 5: Fix Bundler/Tree-Shaking Issues#

If Vercel’s production build is tree-shaking FontAwesomeIcon, explicitly mark icons as used to prevent bundlers from removing them.

For Next.js Users:#

Add @fortawesome packages to next.config.js to exclude them from tree-shaking:

// next.config.js  
module.exports = {  
  webpack: (config) => {  
    config.externals = [...config.externals, '@fortawesome/fontawesome-svg-core', '@fortawesome/free-solid-svg-icons'];  
    return config;  
  },  
};

For Vite Users:#

Add @fortawesome to vite.config.ts to preserve imports:

// vite.config.ts  
import { defineConfig } from 'vite';  
 
export default defineConfig({  
  build: {  
    commonjsOptions: {  
      include: ['@fortawesome/**/*'],  
    },  
  },  
});

5. Testing the Fix Locally Before Deploying to Vercel#

To avoid deploying broken code to Vercel, simulate the production environment locally:

Step 1: Run a Production Build#

For most React apps:

# npm  
npm run build  
 
# yarn  
yarn build

For Next.js apps:

npm run build && npm start

Step 2: Check TypeScript Errors in Production Mode#

Use tsc (TypeScript compiler) with your production config to enforce strict checks:

tsc --project tsconfig.prod.json

If no errors appear, the fix is likely successful.

6. Troubleshooting Persistent Errors#

If the error persists, try these advanced fixes:

Check Vercel Build Logs#

Vercel’s build logs often reveal missing dependencies or TypeScript errors. Navigate to your Vercel project → Deployments → Select the failed deployment → Build Logs. Look for lines like:

  • Could not find a declaration file for module '@fortawesome/react-fontawesome'.
  • Module not found: Error: Can't resolve '@fortawesome/free-solid-svg-icons'.

Delete node_modules and package-lock.json#

Corrupted dependencies can cause type mismatches. Reset them with:

rm -rf node_modules package-lock.json  
npm install

Use @fortawesome/react-fontawesome v0.2.x (Legacy Fix)#

If you’re stuck on an older React version (e.g., React 16), try downgrading @fortawesome/react-fontawesome to 0.2.0 (the last version compatible with React 16):

npm install @fortawesome/[email protected]

7. Conclusion#

The Type '{}' is not assignable to type 'ReactNode' error with FontAwesomeIcon in Vercel (but not locally) is almost always caused by TypeScript type mismatches, missing dependencies, or bundling issues in production. By updating Font Awesome packages, fixing type definitions, correcting imports, and aligning TypeScript configurations, you can resolve this error and ensure your icons render reliably in both local and production environments.

8. References#