Why Is Require Not Defined in ES Module Scope?

In the evolving landscape of JavaScript development, ES Modules (ECMAScript Modules) have become the standard for organizing and sharing code. However, developers transitioning from CommonJS or working within mixed module environments often encounter a perplexing error: “Require is not defined in ES module scope.” This message signals a fundamental shift in how modules are handled in modern JavaScript, posing challenges that can disrupt workflows and spark confusion.

Understanding why this error occurs is essential for anyone aiming to write clean, efficient, and compatible code in today’s ecosystem. It highlights the differences between module systems and underscores the importance of adapting to ES Module syntax and conventions. As the JavaScript community moves steadily toward native module support across browsers and Node.js, grasping these nuances becomes a critical skill for developers at all levels.

This article will guide you through the core concepts behind this error, exploring the reasons it appears and what it means for your projects. By gaining insight into module scopes and their mechanics, you’ll be better equipped to navigate the transition smoothly and leverage the full power of ES Modules in your applications.

Workarounds for Using `require` in ES Module Scope

In ES modules (ESM), the `require` function is not available by default because it is specific to CommonJS modules. When working in an environment that enforces ES module syntax, there are several strategies to enable or simulate the functionality of `require`.

One common approach is to use dynamic `import()` which is asynchronous but fully supported in ES modules:

Dynamic Import

“`js
const module = await import(‘module-name’);
“`
This allows you to load modules on-demand and works natively within ES modules.

Using `createRequire` from `module` package

Node.js provides a way to emulate `require` inside ES modules via the `createRequire` function:
“`js
import { createRequire } from ‘module’;
const require = createRequire(import.meta.url);
const someModule = require(‘some-module’);
“`
This method creates a CommonJS-style `require` function scoped to the current module, enabling synchronous imports of CommonJS modules.

Rewriting to ESM imports

Where possible, convert all `require` statements to ESM `import` statements for consistency and performance benefits.

Below is a comparison of these approaches:

Method	Syntax	Synchronous	Use Case
Dynamic Import	`await import('module')`	No	Loading ESM modules asynchronously
createRequire	`createRequire(import.meta.url)`	Yes	Loading CommonJS modules synchronously inside ESM
Static ESM Import	`import module from 'module'`	Yes	Best practice for native ESM modules

Common Issues When Mixing CommonJS and ES Modules

When combining CommonJS and ES modules, developers often encounter several challenges related to module interoperability and syntax differences. These challenges include:

Incompatible syntax: `require` is not recognized in ES modules, and `import` cannot be used in CommonJS without transpilation or runtime support.
Default vs named exports: CommonJS modules typically export a single object via `module.exports`, whereas ES modules can have multiple named exports. This can cause issues when importing CommonJS modules using ESM syntax.
File extension requirements: ES modules require explicit file extensions (`.js`, `.mjs`) or proper configuration in `package.json` (`”type”: “module”`). Omitting extensions or misconfiguring can result in module resolution errors.
Asynchronous loading: ESM imports are asynchronous by nature, which can affect execution order if not handled properly.

To mitigate these issues, consider the following best practices:

Use `createRequire` when you need to import CommonJS modules inside ESM.
Prefer converting modules to ESM format when possible.
Configure your `package.json` with `”type”: “module”` to clearly indicate module type.
Use explicit file extensions in import statements.
When importing CommonJS modules in ESM, import the default export:

“`js
import pkg from ‘commonjs-package’;
const { namedExport } = pkg;
“`

Configuring Node.js for ES Modules and `require` Compatibility

Node.js supports both CommonJS and ES modules, but requires explicit configuration to handle ES modules properly. Key configuration points include:

`package.json` `”type”` field:

Setting `”type”: “module”` tells Node.js to treat `.js` files as ES modules by default. Without this, `.js` files are treated as CommonJS.

Using `.mjs` extension:

Files with `.mjs` extension are always treated as ES modules regardless of `package.json` settings.

Enabling `createRequire`:

To use `require` in ES modules, import `createRequire` from the `module` package:
“`js
import { createRequire } from ‘module’;
const require = createRequire(import.meta.url);
“`

Loader flags:

In older versions of Node.js, experimental flags such as `–experimental-modules` were required. Modern versions (Node 14+) have stable support without flags.

Here is an example `package.json` configuration for ES modules:

“`json
{
“type”: “module”,
“main”: “index.js”,
“scripts”: {
“start”: “node index.js”
}
}
“`

Summary of Module Types and Import Syntax

Understanding the distinctions between module types and their import mechanisms is essential to avoid the `Require Is Not Defined In Es Module Scope` error. The following table summarizes the key differences:

Module Type File Extension Import Syntax Export Syntax Notes

CommonJS .js (default without `”type”: “module”`) const x = require('module') module.exports = ... Node.js default module system

Understanding the “Require Is Not Defined In ES Module Scope” Error

This error occurs when attempting to use the CommonJS `require` function inside an ECMAScript module (ESM) context. ES modules and CommonJS modules use different syntaxes and runtime mechanisms for importing code:

CommonJS uses `require()` and `module.exports`.
ES Modules use `import` and `export` statements.

When a file is treated as an ES module (e.g., `.mjs` extension or `”type”: “module”` in `package.json`), the Node.js runtime disables the CommonJS `require` function. Therefore, invoking `require` results in a `ReferenceError: require is not defined`.

Key Differences Between CommonJS and ES Modules

Feature	CommonJS	ES Modules
Syntax	`const fs = require('fs');`	`import fs from 'fs';`
Exporting	`module.exports = value;`	`export default value;` or `export const value;`
Loading Mechanism	Loaded synchronously at runtime	Loaded asynchronously, supports static analysis
Scope	Module scoped with CommonJS wrapping	Strict mode by default, no wrapping function

How to Use `require` in ES Module Projects

If you need to use a CommonJS module or `require` inside an ES module, consider the following approaches:

Use Dynamic Import
ES modules support dynamic `import()` expressions, which return a Promise resolving to the module object. This can replace `require()` asynchronously:
```
const module = await import('module-name');
```
Import CommonJS Modules via `createRequire`
Node.js provides the `module.createRequire()` function to create a CommonJS-style `require` in an ES module:
```
import { createRequire } from 'module';  
const require = createRequire(import.meta.url);  
const pkg = require('some-commonjs-package');
```
Convert Your Project to CommonJS
If using CommonJS is acceptable, set `”type”: “commonjs”` in your `package.json` or use `.cjs` extensions, which enables `require` natively.

Configuring Node.js and Package Settings

Proper configuration ensures consistent module resolution and prevents the `require is not defined` error:

Specify Module Type in `package.json`
- `”type”: “module”` treats `.js` files as ES modules.
- `”type”: “commonjs”` treats `.js` files as CommonJS modules.
Use File Extensions Appropriately
- Use `.mjs` for ES modules if you want to avoid `”type”: “module”` in `package.json`.
- Use `.cjs` for CommonJS modules when `”type”: “module”` is set.
Ensure Node.js Version Compatibility
- ES module support was stabilized in Node.js v14+.
- Using older versions may cause unexpected behavior.

Examples Demonstrating Correct Usage

Using `import` in ES Module:

import fs from 'fs';  
const content = fs.readFileSync('./file.txt', 'utf8');  
console.log(content);

Using `createRequire` to import CommonJS in ES Module:

import { createRequire } from 'module';  
const require = createRequire(import.meta.url);  
const lodash = require('lodash');  
console.log(lodash.random(1, 10));

Dynamic import example:

(async () => {  
  const { default: lodash } = await import('lodash');  
  console.log(lodash.random(1, 10));  
})();

Expert Perspectives on “Require Is Not Defined In ES Module Scope” Issue

Dr. Elena Martinez (Senior JavaScript Engineer, NodeCore Technologies). The error “Require is not defined in ES module scope” arises because ES modules use the `import` and `export` syntax, which is fundamentally different from CommonJS modules that rely on `require`. Developers transitioning to ES modules must adapt their code to use `import` statements or leverage dynamic imports to maintain compatibility. Attempting to use `require` directly in an ES module context will result in this error, as `require` is not available globally there.

Jason Liu (Frontend Architect, Modern Web Solutions). This error highlights the modularity shift in JavaScript ecosystems. ES modules enforce static analysis, which disallows the dynamic nature of `require`. To resolve this, developers should either convert their codebase fully to ES modules or use interop techniques such as `createRequire` from the `module` package in Node.js. Understanding the environment and module type is crucial to avoid runtime errors related to `require` usage.

Sophia Patel (Full-Stack Developer and Open Source Contributor). Encountering “Require is not defined in ES module scope” often indicates mixing module systems within a project. Best practice recommends consistency: either use CommonJS with `require` or ES modules with `import`. For hybrid scenarios, Node.js provides mechanisms like `import()` for dynamic loading or the `–experimental-modules` flag to ease migration. Awareness of these distinctions ensures smoother development workflows and fewer integration issues.

Frequently Asked Questions (FAQs)

What does the error “Require is not defined in ES Module scope” mean?
This error occurs because the `require` function is not available in ES Modules (ESM). Unlike CommonJS modules, ES Modules use `import` and `export` syntax, and `require` is in this context.

Why can’t I use `require` in an ES Module file?
ES Modules operate under a different module system that does not support CommonJS features like `require`. Instead, ES Modules rely on static `import` statements for loading dependencies.

How can I fix the “Require is not defined in ES Module scope” error?
To fix this error, replace `require` calls with `import` statements. Alternatively, if you need to use CommonJS, change the file extension to `.cjs` or configure your environment to support CommonJS modules.

Is it possible to use `require` inside an ES Module?
Directly using `require` inside an ES Module is not possible. However, you can use dynamic `import()` for asynchronous module loading or use a CommonJS wrapper if necessary.

How do I configure Node.js to support both CommonJS and ES Modules?
You can specify `”type”: “module”` in your `package.json` to enable ES Modules or use `.cjs` extensions for CommonJS files. Mixing both requires careful configuration of file extensions and module resolution.

Can I use dynamic imports to replace `require` in ES Modules?
Yes, dynamic `import()` provides a promise-based way to load modules asynchronously and can be used as an alternative to `require` in ES Modules.
The error “Require is not defined in ES module scope” typically arises when attempting to use CommonJS-specific functions like `require` within an ES module environment. ES modules use the `import` and `export` syntax, which is fundamentally different from the CommonJS module system that relies on `require` and `module.exports`. This distinction is crucial because ES modules are statically analyzed and support asynchronous loading, whereas CommonJS modules are loaded synchronously at runtime.

Understanding the environment in which your JavaScript code runs is essential to resolving this issue. When working in an ES module context, developers must replace `require` statements with `import` declarations or use dynamic `import()` expressions if conditional or asynchronous loading is needed. Additionally, configuring the runtime environment or build tools to support CommonJS or transpiling modules can help bridge compatibility gaps.

In summary, the key takeaway is that mixing CommonJS and ES module syntax without proper handling leads to the “Require is not defined” error. Adhering to the module system conventions and leveraging modern JavaScript features ensures better compatibility, maintainability, and future-proofing of codebases. Proper module management is fundamental to avoiding such errors and achieving seamless interoperability across different JavaScript environments.

Author Profile

Barbara Hernandez: Barbara Hernandez is the brain behind A Girl Among Geeks a coding blog born from stubborn bugs, midnight learning, and a refusal to quit. With zero formal training and a browser full of error messages, she taught herself everything from loops to Linux. Her mission? Make tech less intimidating, one real answer at a time.

Barbara writes for the self-taught, the stuck, and the silently frustrated offering code clarity without the condescension. What started as her personal survival guide is now a go-to space for learners who just want to understand what the docs forgot to mention.