NestJS serving JSON and adds a "default" section repeating the JSON - nestjs

Question

I have a strange behaviour on an endpoint in NestJS serving a piece of JSON.
The JS with the JSON object is exporting
module.exports = Object.freeze({
translation: {
TestMessage: 'Bienvenue à React et react-i18next'
}
});
The result on the Client is:
{
"translation": {
"TestMessage": "Bienvenue à React et react-i18next"
},
"default": {
"translation": {
"TestMessage": "Bienvenue à React et react-i18next"
}
}
}
The question is where is the "default" coming from?
To paint the whole picture, below the module, controller and service:
Module
import { Module } from '#nestjs/common';
import { LoggerService } from '#modules/logger';
import { I18nController } from './i18n.controller';
import { I18nService } from './i18n.service';
#Module({
controllers: [I18nController],
providers: [I18nService, LoggerService],
exports: [I18nService]
})
export class I18nModule {}
Controller
import { Controller, Get, Param } from '#nestjs/common';
import { LoggerService } from '#modules/logger';
import { I18nService } from './i18n.service';
#Controller('i18n')
export class I18nController {
constructor(private logger: LoggerService, private i18nService: I18nService) {
this.logger.setContext(I18nController.name);
}
#Get('/:lang')
async getLanguage(#Param('lang') lang: string) {
console.log(lang);
return await this.i18nService.findOneByLanguageCode(lang);
}
}
Service
import { Injectable } from '#nestjs/common';
import { access } from 'fs/promises';
import { constants as fsconstants } from 'fs';
#Injectable()
export class I18nService {
async findOneByLanguageCode(language: string): Promise<any | null> {
const languagefile = __dirname + '/../../public/languages/' + language + '.js';
await access(languagefile, fsconstants.R_OK);
return await import(languagefile);
}
}
From the Client I do a simple http://localhost:3001/i18n/fr-FR
and get the above result.
Again, where is the 'default' section coming from?

Answer 1

There should be esModuleInterop enabled in your tsconfig.json
https://www.typescriptlang.org/tsconfig#esModuleInterop
a default import like import moment from "moment" acts the same as const moment = require("moment").default
That's why you have default object exist.
tsconfig.json
{
"compilerOptions": {
"esModuleInterop": true, // change it to false or remove it
}
}