node.js 13 - import is not working properly

Question

$ node --version v13.8.0

Let's create three files:

// package.json
{
  "type": "module"
}

// foobar.js 
function foo() { console.log('foo') }
export default {foo}

// index.js 
import Foo from './foobar.js';
Foo.foo();

Run index.js

$ node index.js
(node:22768) ExperimentalWarning: The ESM module loader is experimental.
foo

All working.

And now changing './foobar.js'; to './foobar';

// index.js 
import Foo from './foobar';
Foo.foo();

And we get an error!

(node:22946) ExperimentalWarning: The ESM module loader is experimental.
internal/modules/esm/resolve.js:58
  let url = moduleWrapResolve(specifier, parentURL);
            ^
Error: Cannot find module /foobar imported from /index.js

There is no other files in directory.

Why does it happens? Why import without extension doesn't work?

UPDATE: https://nodejs.org/api/esm.html

package.json "type" field

Files ending with .js or lacking any extension will be loaded as ES modules when the nearest parent package.json file contains a top-level field "type" with a value of "module".

So './foobar' must work.

UPDATE 2:

I believe what the documentation call "extensionless files" are literaly files without extensions, not files imported without extensions.

For example, if you import your file with import Foo from './foobar';, and you file is called foobar without the .js extension, it will work fine.

Thanks to @Seblor

Answer 1

Looking at the documentation, in the category Differences Between ES Modules and CommonJS , and more precisely at the "Mandatory file extensions" section, it says that the .js file extension must be present to make the import work :

A file extension must be provided when using the import keyword. Directory indexes (eg './startup/index.js') must also be fully specified.

This behavior matches how import behaves in browser environments, assuming a typically configured server.

I am not sure why your last question is about the import without extention not working anymore . I guess you have been working at some point with a transpiler like babel that will resolve the files without the extensions.

Edit :

I believe what the documentation call "extensionless files" are literaly files without extensions, not files imported without extensions.

For example, if you import your file with import Foo from './foobar'; , and you file is called foobar without the .js extension, it will work fine.