error [err_require_esm]: require() of es module: How to Fix and Prevent

If you’re working with Node.js or JavaScript and encounter the “error [err_require_esm]: require() of es module,” you’re not alone. This is a common issue when developers mix CommonJS and ES modules in their projects. While this can be frustrating, the good news is that it’s entirely fixable. In this article, we’ll walk through what causes this error, how to prevent it, and actionable solutions to get your code running smoothly.

The root cause of this error stems from Node.js treating ES modules and CommonJS modules differently. If you’re using require() to import an ES module, Node.js will throw the error [err_require_esm]. In modern JavaScript, the preferred import method for ES modules is import, which leads to this conflict. Below, we’ll break down exactly how to manage your modules to ensure compatibility and avoid future errors.

Why Does the Error [err_require_esm] Occur?

The “error [err_require_esm]: require() of ES module” occurs primarily because of the differences between how Node.js handles CommonJS and ES module systems. This error is common when developers attempt to use the require() function, which is part of CommonJS, to load an ES module. Below are the key reasons why this error occurs:

1. Incompatibility Between CommonJS and ES Modules:Node.js initially supported only CommonJS modules, which use require() and module. exports for importing and exporting functions, objects, and values. ES modules, on the other hand, use import and export syntax, introduced in ECMAScript 2015 (ES6). These two module systems are not fully compatible with each other, and this is the root cause of the error. Attempting to use require() with an ES module leads to the “[err_require_esm]” error because Node.js expects ES modules to be loaded using the import syntax.

2. Incorrect Package Configuration: In some cases, the package.json file isn’t correctly configured to indicate whether the project is using ES modules or CommonJS modules. When “type”: “module” is not set in the package.json, Node.js treats all files as CommonJS by default. If you then try to import an ES module using require(), the system will throw the error. The lack of clear instructions in the package.json file leads to a miscommunication between the code and Node.js on how to handle the modules.
3. Third-Party Dependencies: Many third-party libraries and older Node.js modules still use CommonJS, while newer libraries have transitioned to ES modules. If your project involves a mix of dependencies that use both systems, the conflict can trigger the “[err_require_esm]” error. For example, if you attempt to import an ES module in a project where most modules are using CommonJS, the system will generate an error due to the incompatibility.
4. File Extensions and ES Module Detection: Another reason the error might occur is due to file extensions. Node.js uses .mjs to explicitly mark files as ES modules. If you’re working with .js files but expecting Node.js to treat them as ES modules without proper configuration, it could result in the error. Node.js may still default to treating .js files as CommonJS unless directed otherwise in the package.json.
5. Node.js Version: The version of Node.js you’re working with can also lead to this error. Support for ES modules in Node.js was fully stabilized in version 12. If you’re using an older version of Node.js, ES module handling may not work as expected, leading to this error when attempting to use modern syntax.

How do I fix the [err_require_esm] error?

Fixing the “[err_require_esm]: require() of es module” error involves understanding the root cause of the issue and applying the correct solutions based on your project’s structure. This error occurs when trying to use the CommonJS require() function to load an ES module, which is incompatible due to differences in how Node.js handles these two module systems. Here are the steps to resolve the error:

1. Switch to the import Syntax

The simplest and most direct way to fix this error is by switching from the CommonJS require() function to the ES module import syntax. ES modules use import and export, while CommonJS relies on require() and module.exports. If you are working with ES modules, using the correct import method is essential to avoid the “[err_require_esm]” error.

2. Update package.json Configuration

In some cases, the issue may arise from how your project is configured in the package.json file. Node.js defaults to using CommonJS modules unless otherwise specified. To indicate that your project uses ES modules, you need to set the “type”: “module” field in your package.json. This tells Node.js to interpret your files as ES modules and prevents the system from trying to use require() with an ES module. Make sure this configuration is in place if you plan to use modern ES syntax throughout your project.

3. Use Dynamic Imports

If you’re working in an environment where you need to dynamically load modules, you can use the ES module dynamic import() syntax. This approach allows you to import ES modules on the fly, avoiding the need to use require() and eliminating the error. Dynamic imports are particularly useful when modules are loaded conditionally or asynchronously.

4. Check for Inconsistent Module Use

Another important step is to ensure consistency in how you manage modules across your entire project. If you are mixing CommonJS and ES modules, you are more likely to encounter this error. Standardize your codebase to use either CommonJS or ES modules, or handle them separately if mixing is unavoidable. If some dependencies still use CommonJS, you may need to transpile them or use backward-compatible libraries.

5. Rename Files with .mjs Extension

Another workaround is to rename your ES module files with the .mjs extension. This tells Node.js to treat them as ES modules regardless of other configurations. While this isn’t necessary for every project, it can be a quick fix if you’re working with mixed modules and need to signal ES module usage more explicitly.

By following these steps, you can resolve the “[err_require_esm]: require() of es module” error and ensure that your Node.js project runs smoothly without compatibility issues.

The Wrapping Up

Encountering the “error [err_require_esm]: require() of es module” can feel daunting, especially when working with a mix of CommonJS and ES modules. However, by understanding the differences between the two systems, using the correct syntax, and modifying your project configuration where necessary, you can resolve this issue. Standardizing your codebase to use ES modules will future-proof your project and ensure smoother operation moving forward.

FAQ

Can I use both CommonJS and ES modules in the same project?

It’s not recommended to mix them, but you can with specific configurations like setting “type”: “module” in package.json. However, standardizing one format is more future-proof.

What does “error [err_require_esm]: require() of es module” mean?

This error occurs when you use require() to load an ES module in Node.js, which only supports import statements for ES modules.