Using esm to Enable ES Modules in Node.js

As Node.js continues to evolve, developers often face compatibility challenges when working with modern JavaScript syntax. One of the most common issues arises when trying to use import and export — the standard ECMAScript (ES) module syntax — in older Node.js environments that only support CommonJS (require/module.exports). This article explains how to use the esm package to bridge that gap, along with practical business and development use cases where this approach can save time and reduce friction in large-scale applications.

Why Use esm?

Before Node.js added native support for ES modules, developers were forced to use CommonJS syntax. However, many modern libraries, frameworks, and tools are now written using ES module syntax. If your existing project still uses CommonJS but you want to import new ES-based modules, you’ll likely face syntax errors like:

SyntaxError: Cannot use import statement outside a module

This is where the esm package comes in. It allows you to run ES module code seamlessly within CommonJS-based projects, enabling a smooth transition toward modern syntax without breaking your existing application.

How esm Works

The esm package acts as a lightweight runtime loader that allows you to use ES modules within a Node.js environment that doesn’t natively support them. It wraps your require calls and compiles import/export syntax on the fly, so you can start using modern JavaScript immediately.

Example Setup

Here’s the simplest way to enable ES module syntax using esm:

// app.js
require = require('esm')(module);
module.exports = require('./index.js');

Now, inside index.js, you can freely use ES module syntax:

// index.js
import express from 'express';

const app = express();
app.get('/', (req, res) => res.send('Hello from ES Modules!'));
app.listen(3000, () => console.log('Server running on port 3000'));

When you run node app.js, the esm package interprets your ES imports correctly. This lets you adopt modern syntax even if your Node.js version or codebase isn’t fully compatible yet.

Real-Life Business Use Case

Imagine you’re maintaining a long-standing enterprise backend system written years ago in CommonJS. Your team wants to integrate new microservices or libraries written in ES modules — for example, a data analytics microservice built by another team using modern tooling.

Instead of rewriting thousands of legacy lines of code or maintaining two separate builds, you can install esm and start importing new ES-based modules immediately:

npm install esm

This reduces development time and technical debt while ensuring your business can evolve faster without breaking production systems.

When Not to Use esm

While esm is a powerful tool, it’s no longer necessary in newer Node.js versions (v12 and above) where ES module support is built-in. If you’re starting a new project, it’s better to use the native approach:

{
  "type": "module"
}

This line in your package.json tells Node.js to interpret your project files as ES modules, eliminating the need for extra dependencies.

Common Errors and Fixes

• Error: TypeError: Function.prototype.apply was called on undefined
  Fix: Ensure esm is installed and the wrapping syntax require = require('esm')(module) is used before importing your files.
• Error: Cannot find module 'esm'
  Fix: Run npm install esm in your project root.

SEO and Discoverability Tips for Developers

Developers often search Google for phrases like:

• “How to use import and export in Node.js”
• “Enable ES modules in Node.js project”
• “SyntaxError: Cannot use import statement outside a module”
• “Using esm in Node.js example”

By understanding how to configure esm and why it matters, you can quickly resolve these issues — saving hours of debugging time and making your codebase more modern, modular, and maintainable.

Key Takeaways

• esm enables ES module syntax in older Node.js projects.
• It acts as a runtime compiler, letting you use import/export seamlessly.
• Ideal for transitioning legacy CommonJS apps without full rewrites.
• Modern Node.js versions (v12+) can natively use ES modules via "type": "module" in package.json.

Whether you’re maintaining enterprise software or building small business applications, learning to integrate ES modules effectively helps you stay current with the latest JavaScript standards — and that makes your development workflow faster, cleaner, and more scalable.

Author’s Note: Always test your build setup after integrating esm and consider upgrading your Node.js environment for native support as part of long-term modernization plans.