How to use mjs module in mocha?

[wnghdcjfe]

I try to use mocha like this for this reference
https://mochajs.org/#nodejs-native-esm-support

main.mjs

import {add} from './add.mjs';
import assert from 'assert';

it('should add to numbers from an es module', () => {
  assert.equal(add(3, 5), 8);
});

add.mjs

export function add(a, b){
    return a + b; 
} 

command

mocha main.js --experimental-modules
mocha main.js --extension mjs

But both of them is not working

I also found the npm link
https://www.npmjs.com/package/mjs-mocha
But Can't Mocha just alone do that?

version

• mocha : v7.2.0
• node : v10.15.1

[juergba]

Mocha supports ES modules only from Node.js v12.11.0 and above. To enable this in versions smaller than 13.2.0, you need to add --experimental-modules when running Mocha. From version 13.2.0 of Node.js, you can use ES modules without any flags.

[juergba]

duplicate of #4297

[wnghdcjfe]

Thanks a lot @juergba. Have nice a day

[meszaros-lajos-gyorgy]

For anyone googleing why --watch is not working with mjs files, the docs state, that this is a known limitation: https://github.com/mochajs/mocha/blob/master/docs/index.md#current-limitations

Watch mode does not support ES Module test files

One possible workaround is to use nodemon and it's --exec flag:

"scripts": {
  "unit": "mocha --experimental-modules --no-warnings test/**/*.spec.mjs",
  "unit:watch": "nodemon --exec \"npm run unit\" --watch test/**/*.spec.mjs",
}