ah-theyre-here-esm-nodejs

Code accompanying my talk "Aaaaaaaaaaaaaah, They’re Here! ES Modules in Node.JS", whose slides can be found here

Installing

You will need a Node.js version >= 13.2.

First, you install:

$ npm ci
...

Then, you build:

$ npm run build
...

Running the tests

This repository has code in src that is fully checked by tests in the test dir. To run the test, use:

$ npm test
...

About the source code samples directories

The src directory contains all the code samples found in the talk:

• 01-what-are-es-modules: code that shows a sample of ES module syntax, along with its equivalent CommonJS code. This sample is not comprehensive by any moeans
• 02-strict: code that shows that ES modules are strict by definition, while CommonJS is not.
• 03-esm-is-browser-compatible: code that shows that the same ES module code can be used both in the browser and in Node.js, including the use of "import maps".
• 04-esm-is-statically-parsed code that shows that ES module problems are caught statically before execution of said code.
• 05-esm-is-async: code that shows sample "top-level await" code. This code does not (yet) run in Node.js and is not tested.
• 06-exports: code that shows how the "exports" field in package.json works
• 07-conditional-exports: code that shows how conditional exports work, and a sample dual-mode library that is automatically created from ESM code. See this section for more explanations.
• 08-migration: code that shows how to migrate CommonJS code to ES module code, bottom up or top down.

Dual-mode packages

See this package source code for how to create an ESM package and automatically convert it to a dual-mode package with additional CJS files.

In essence:

• The esm directory contains the source code itself, and a package.json that has "type": "module" in it. The "type: "module" is necessary because the names of the files in ESM and CJS must stay the same, and this is only possible if the extension is .js in both cases.
• The build script uses babel to transpile the esm directory.
• The .babelrc file includes only the specific plugins necessary to transpile import to package.json.
• The package.json file includes the dependencies needed on babel* packages.
• The package.json includes the "exports" for the dual-mode entry points in the esm and cjs directories.