Using ES6 modules in Express

Question

Is there a way to

1. write my code using ES6 modules in Express app;
2. without reverting to babel or @std/esm ?

once I am committed to app.js of Express, I can't find a way to get out of it.

This seems like something that should be already on the web, but all I can find is above options (transpiling, esm).

Answer 1

With node.js, you HAVE to tell it that your main file you are loading is an ESM module. There are a couple ways to do that. The simplest is to just give the main file a .mjs file extension.

// app.mjs

import express from 'express';

const app = express();

app.get("/", (req, res) => {
    res.send("hello");
});

app.listen(80);

Then, start your program with:

node app.mjs

This works - I just ran it with node v14.4.0:. The others ways to do it are discussed in the link I previously gave you here. Per that documentation, there are three ways to specify you are loading an ESM module as the top-level module file:

1. Files ending in .mjs.

2. Files ending in .js when the nearest parent package.json file contains a top-level field "type" with a value of "module".

3. Strings passed in as an argument to --eval, or piped to node via STDIN, with the flag --input-type=module.