Copying my answer from that old post with all the high vote, old info...
The most important thing to know is that ES6 modules are, indeed, an official standard, while CommonJS (Node.js) modules are not.
In 2019, ES6 modules are supported by 84% of browsers. While Node.js puts them behind an --experimental-modules flag, there is also a convenient node package called esm, which makes the integration smooth.
Another issue you're likely to run into between these module systems is code location. Node.js assumes source is kept in a node_modules
directory, while most ES6 modules are deployed in a flat directory structure. These are not easy to reconcile, but it can be done by hacking your package.json
file with pre and post installation scripts. Here is an example isomorphic module and an article explaining how it works.