Question: Loading ES6 modules --experimental-modules

[Legends]

• Version: 9.7.1
• Platform: Win 10 x64, VsCode 1.21
• Subsystem: -

Works fine with require.
Trying to use ES6 module import format in node.js application, but getting errors:

launch.json:

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "node",
            "request": "launch",
            "name": "Launch Program",
            "program": "${workspaceFolder}\\src\\index.js",
            "runtimeArgs": [
                "--experimental-modules"
            ]           
        }
    ]
}

ModulesFile.js
export class X...

export class Y ...

Index.js
import X from"../samples/ModulesFile";

Result:

node --experimental-modules --inspect-brk=44256 src\index.js
Debugger listening on ws://127.0.0.1:44256/746a3126-db49-402c-b2b7-5cfee4c55c92
(node:51108) ExperimentalWarning: The ESM module loader is experimental.

null: SyntaxError: Unexpected identifier

[devsnek]

your files with es module syntax in them will need to be named with .mjs not .js

[ChALkeR]

https://nodejs.org/api/esm.html#esm_enabling

Once this has been set, files ending with .mjs will be able to be loaded as ES Modules.

Upd: I was late by a second :-).

[Legends]

I changed my entry file to be *.mjs.
Now I get:

see

Error: linking error, not in local cache

[devsnek]

this was fixed on node 9.8.0

[Legends]

ReferenceError: require is not defined

Too experimental.... switching back to require...

[ChALkeR]

@Legends require does not exist in ESM, i.e. in *.mjs files — use import there.
You can still use require in *.js files.

That is intended to be that way and does not come from the «experimental» stability level 😉.

[Legends]

Yeah, I had a require nested in the code...
What about the future, do we have to rename the ".js" files to ".mjs", when using ESM?
Or is this only during "experimental mode"?

[devsnek]

@Legends the future isn't 100% known yet, you can follow along at https://github.com/nodejs/modules.

[cliffhall]

https://nodejs.org/api/esm.html#esm_enabling

The --experimental-modules flag can be used to enable support for ECMAScript modules (ES modules).

Actually, the doc says you can avoid naming with .mjs if you have a package.json appropriately configured nearby:

Once enabled, Node.js will treat the following as ES modules when passed to node as the initial input, or when referenced by import statements within ES module code:

Files ending in .mjs.

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

This worked for me at:

node --version 
v12.6.0

I just added a package.json in the same folder as my script like this:

{
  "type": "module"
}

I ran my script with the --experimental-modules flag