Solving the require is not defined Error in Express.js

Описание: Learn how to fix the `require is not defined` error in your Express.js application by converting modules correctly and understanding the Node.js environment.
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This video is based on the question https://stackoverflow.com/q/73139407/ asked by the user 'Amine Ladrani' ( https://stackoverflow.com/u/19633343/ ) and on the answer https://stackoverflow.com/a/73139564/ provided by the user 'maximilian pult' ( https://stackoverflow.com/u/10155408/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the require is not defined Error in Express.js: A Comprehensive Guide

When working with Express.js, one common issue developers often encounter is the error message saying that require is not defined. This can be particularly frustrating for those who are accustomed to using CommonJS syntax. In this guide, we will explore this issue and provide effective solutions to get your Express.js application up and running smoothly.

Understanding the Problem

If you have recently switched your project to use ES Modules by adding "type": "module" to your package.json, you may have noticed that the require statement no longer works as it did before. This change affects how Node.js handles imports and exports in your JavaScript files.

Example of the Problematic Code

Consider the following code sample from an Express.js application:

[[See Video to Reveal this Text or Code Snippet]]

In this example, the require statement is leading to an error because the file is expected to be using ES Module syntax instead of CommonJS.

Solution Steps

To resolve the require is not defined issue in your Express.js application, follow these steps:

Step 1: Rename Your Files

Change your file extension from .mjs to .js. This might seem counterintuitive since you are using ES Modules, but renaming it back to .js can help resolve the issue temporarily.

Step 2: Modify Your Command to Start the Application

You will want to run the application using the following command:

[[See Video to Reveal this Text or Code Snippet]]

Always ensure that you are using the exact filename in the command. If your file is named app.js, that is what you should call.

Step 3: Convert to ES Module Syntax

If you prefer to use ES Module syntax, update your imports as follows:

[[See Video to Reveal this Text or Code Snippet]]

Step 4: Check Your package.json Settings

Make sure your package.json includes the type definition. It should look something like this:

[[See Video to Reveal this Text or Code Snippet]]

This ensures that Node.js treats your files as ES Modules.

Conclusion

The require is not defined error in Express.js occurs primarily due to the transition from CommonJS to ES Modules. By renaming your file, modifying how you start your application, or converting your imports to use ES Module syntax, you can effectively resolve this issue. If you continue to experience problems, always double-check your package.json configurations to ensure you are set up correctly.

By following the steps outlined above, you will be able to navigate this common obstacle in Express.js development and continue building your applications with confidence.