load-esm

load-esm is a utility for dynamically importing pure ESM (ECMAScript Module) packages in CommonJS TypeScript projects.

This resolves the error:

Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: No "exports" main defined in...

Installation

npm install load-esm

or

yarn add load-esm

Usage

Here’s a conceptual example demonstrating how to use load-esm to dynamically load an ESM module in a CommonJS project:

import {loadEsm} from 'load-esm';

/**
 * Import 'file-type' ES-Module in CommonJS Node.js module
 */
(async () => {
  const esmModule = await loadEsm('esm-module');
})();

To import the typings you need do the following:

import {loadEsm} from 'load-esm';
(async () => {
const esmModule = await loadEsm<typeof import('esm-module')>('esm-module');
})();

A concrete example loading file-typ, a pure ESM package:

import {loadEsm} from 'load-esm';

/**
 * Import 'file-type' ES-Module in CommonJS Node.js module
 */
(async () => {
    try {
        // Dynamically import the ESM module, including types
        const { fileTypeFromFile } = await loadEsm<typeof import('file-type')>('file-type');

        // Use the imported function
        const type = await fileTypeFromFile('fixture.gif');
        console.log(type);
    } catch (error) {
        console.error('Error importing module:', error);
    }
})();

API

loadEsm<T = any>(name: string): Promise<T>

Dynamically imports an ESM module.

Parameters

• name (string): The name or path of the module to load.

Returns

• A Promise<T> that resolves to the imported module object.

How It Works

Using await import in a CommonJS TypeScript project poses challenges because the TypeScript compiler transpiles import() statements to require() calls when module is set to CommonJS in tsconfig.json. This behavior conflicts with the dynamic nature of import() used for ESM.

Workarounds, such as wrapping the import() statement within eval() or similar constructs, can prevent TypeScript from transpiling it, but these approaches are clunky and error-prone.

The utility of load-esm bypasses the TypeScript compiler by executing the import() outside the compilation scope. By doing so, it maintains the intended behavior of import() for loading ESM modules dynamically, providing a clean and effective solution for such scenarios.

Compatibility

• Node.js: Requires Node.js 13.2.0 or later, as import() is only supported in these versions and beyond.
• TypeScript: Fully typed and compatible with TypeScript.

License

MIT