How to use ES6 modules in node.js? [duplicate]

Question

There is something I fail to understand with ES6 modules in the context of node.js.

Let's say I have this simple node app. It is based on an iisnode example but I added an import at the top.

hello.js:

import mod1 from './module1'; var http = require('http'); http.createServer(function (req, res) { res.writeHead(200, {'Content-Type': 'text/html'}); res.end(mod1.data); }).listen(process.env.PORT);

This will result in SyntaxError: Cannot use import statement outside a module

However if I rename hello.js to hello.mjs I get the following error: Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: C:\Program Files\iisnode\www\hellomodules\hello.mjs

Seems like a catch to me, what is the way out?

(iisnode version is 0.2.26, node version is v13.8.0)

@Hogan, I do not see how that applies in my case. The issue you linked to was a case of misleadingly worded error message which was fixed way back then. Furthermore, std/esm or esm should not be needed at all since nodejs 12. — g.kertesz
– g.kertesz, Commented Feb 12, 2020 at 15:57

André Machado · Accepted Answer · 2020-06-09 22:46:16Z

Solving this issue:

If the file format is .js, or if the Node version < 13, add "type": "module" in package.json
To allow debug, add "runtimeArgs": ["--experimental-modules"] in .vscode/launch.json
Always use the flag --experimental-modules to run: node --experimental-modules hello.mjs

In the newer Node versions it isn't necessary to take these steps

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