Resolving the "promisify is not a function" Error in MongoDB Node.js Applications

When working with MongoDB in Node.js applications, you might encounter the following error:

Uncaught TypeError: (0 , util_1.promisify) is not a function
at ../../node_modules/.pnpm/mongodb@6.15.0/node_modules/mongodb/lib/utils.js

This cryptic error can be frustrating to debug, especially if you’re using MongoDB with a framework or other tools. Let’s break down what causes this error and how to fix it.

Understanding the Error

The error occurs because the MongoDB driver is trying to use Node.js’s built-in util.promisify function but can’t locate it properly. This typically happens in one of these scenarios:

1. Environment incompatibility: Running MongoDB code in an environment that doesn’t fully support or provide Node.js utilities
2. Module resolution issues: Problems with how the MongoDB package is being imported or bundled
3. Version conflicts: Mismatches between your MongoDB driver version and Node.js version

In this specific case, the error appears in a project that’s using pnpm (as indicated by the .pnpm in the path) and possibly bundling the code for browser use.

Common Causes

1. Browser Environment Issues

MongoDB is primarily designed for server-side Node.js applications, but many modern frameworks attempt to bundle and run code that might execute in both server and browser environments. The browser doesn’t have Node.js’s util module built in.

2. Bundling Configuration Problems

Tools like Webpack, Rollup, or Vite might not be correctly configured to handle Node.js-specific modules when bundling MongoDB for client-side use.

3. Missing Polyfills

If you’re using MongoDB in a non-Node.js environment, you might need to provide polyfills for Node.js core modules.

Solutions

Here are several approaches to resolve this error:

Solution 1: Ensure Server-Side Only Usage

Make sure MongoDB operations only run server-side, not in browser code:

// For Next.js or similar frameworks
export async function getServerSideProps() {
  // MongoDB code here - runs only on the server
  const client = await MongoClient.connect(uri);
  // ...
  return { props: { data } };
}

Solution 2: Add Required Polyfills

If you must use MongoDB-related code in a browser-compatible bundle, add polyfills for Node.js utilities:

// In your webpack or bundler config
module.exports = {
  // ...
  resolve: {
    fallback: {
      util: require.resolve('util/'),
      stream: require.resolve('stream-browserify'),
      buffer: require.resolve('buffer/')
    }
  },
  plugins: [
    new webpack.ProvidePlugin({
      process: 'process/browser',
      Buffer: ['buffer', 'Buffer']
    })
  ]
};

Solution 3: Use MongoDB Data API Instead

For applications needing MongoDB access from browser environments, consider using MongoDB’s Data API instead of the direct driver:

async function fetchData() {
  const response = await fetch('https://data.mongodb-api.com/app/<App ID>/endpoint/data/v1/action/find', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'api-key': '<Your API Key>'
    },
    body: JSON.stringify({
      dataSource: 'myCluster',
      database: 'myDb',
      collection: 'myCollection',
      filter: { status: 'active' }
    })
  });
  return await response.json();
}

Solution 4: Update Your Dependencies

Ensure compatible versions of all packages:

# If using npm
npm update mongodb

# If using pnpm
pnpm update mongodb

# Check your Node.js version
node -v

Remember that MongoDB was designed primarily for server-side use.