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Import vs Require in Node.js

Node.js introduced support for the import statement in Node.js 12, although you need to opt in by setting a package.json configuration option. However, Node.js has no plans to drop support for require() (CommonJS). Which should you use?

Below is a high-level summary of the tradeoffs:

1. ESM import is part of the JavaScript language spec, require() is not.
2. import requires a special configuration option in package.json.
3. import does not support importing JSON files. You'll get a Unknown file extension ".json" error if you try to import a file that ends in .json.
4. Even though ESM modules work in both the browser and Node.js, there's no guarantee that your Node.js code will work in the browser and vice-versa.
5. Several Node.js features don't work with ESM: NODE_PATH, __dirname, __filename, and require.extensions don't work if you opt in to { "type": "module" }.

Recommendations

Even though there are numerous tradeoffs, none of the tradeoffs is sufficiently important for us to recommend using one or the other in all cases. Here's a few reasons why you might prefer one over the other:

1. If you're building a full-stack application and want to use the same syntax all the way through, using ESM imports is a good choice.
2. If your app uses __dirname for relative file paths with fs, you need to use require() or refactor your app.
3. If you rely on importing JSON files (configuration, seed data, etc.) you need to use require(), or refactor your app to instead read JSON files using fs.

For now, Mastering JS will stick to using require(), because that's what we're used to and we don't know of a compelling enough reason to switch.

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