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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)

g.kertesz
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  • https://github.com/nodejs/node/issues/17063#issuecomment-344782748 – Hogan Feb 12 '20 at 15:06
  • @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 Feb 12 '20 at 15:57
  • ok -- it is the same error message you posted. – Hogan Feb 12 '20 at 16:13

1 Answers1

3

Solving this issue:

  1. If the file format is .js, or if the Node version < 13, add "type": "module" in package.json
  2. To allow debug, add "runtimeArgs": ["--experimental-modules"] in .vscode/launch.json
  3. 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

André Machado
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