As the JavaScript ecosystem continues to evolve, the concept of ECMAScript Modules (ESM) is becoming more popular. ESM allows developers to write code in a modular way and import and export components between different files, making code maintenance and reuse easier. In this article, we'll explore what ESM is and how to use it in Next.js

What is ESM?

ECMAScript Modules (ESM) is a standardized format for organizing and sharing code in JavaScript applications. ESM allows you to write modular code by breaking it up into small, reusable pieces, which can be easily imported and exported between different files.

Before ESM, developers used CommonJS, which is still the default module system in Node.js. However, CommonJS has some limitations, such as the inability to perform static analysis on modules, which can result in slower module loading times.

ESM provides a solution to these problems by using a syntax that is more similar to the syntax of the web. ESM uses the import and export keywords to import and export modules, respectively.

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How to Use ESM in Next.js

Next.js has built-in support for ESM, which means that you can use ESM in your Next.js projects without any additional configuration.

To use ESM in your Next.js project, you can create a file with a .mjs extension, which indicates that it is an ESM file. You can then use the import and export keywords to import and export modules, respectively.

Here's an example of how to create an ESM file in Next.js:

// pages/product/[productId].js

import { getServerSideProps } from 'next';
import { getProductById } from '../../api/products';

function ProductPage({ product }) {
  return (
    <div>
      <h1>{product.name}</h1>
      <p>{product.description}</p>
    </div>
  );
}

export async function getServerSideProps(context) {
  const { productId } = context.params;
  const product = await getProductById(productId);

  return {
    props: {
      product,
    },
  };
}

export default ProductPage;

You can then import this module in another ESM file in your Next.js project:

// index.mjs
import { add } from "./utils.mjs";

console.log(add(1, 2)); // Output: 3

By default, Next.js will treat .js files as CommonJS modules and .mjs files as ESM modules. However, you can also configure Next.js to use ESM for .js files by adding the following to your next.config.js file:

// next.config.js
export default {
  experimental: {
    esmExternals: true,
  },
};

This will tell Next.js to treat .js files as ESM modules.

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Benefits of Using ESM in Next.js

Using ESM in Next.js can provide several benefits, including:

1. Faster module loading times: ESM allows for faster module loading times compared to CommonJS because it enables static analysis of modules, which allows for more efficient loading of modules.

2. Improved code organization: ESM allows you to write modular code, which can make your codebase more organized and easier to maintain.

3. Compatibility with the web: ESM is more similar to the syntax of the web, which makes it easier to use across different environments and tools.

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Conclusion

ECMAScript Modules (ESM) is a standardized format for organizing and sharing code in JavaScript applications. In Next.js, you can use ESM to write modular code and improve the organization and maintainability of your codebase. By using ESM in Next.js, you can also benefit from faster module loading times and compatibility with the web.