Babel Not Working Outside of Main Node.js App

Question

My Express.js server is currently being started by running start.js, which in turn runs server.js (code below). For example,

nodemon start.js

Problem: When I try to run the file at src/lib/seed_database.js using

node seed_database.js

we get the errors showing that babel is not transpiling any JS files, such as

SyntaxError: Unexpected token 'export'

What is the recommended way to get babel to work on a file other that server.js?

Environment

Node 13.7.0
Mac OS X 10.15.2
@babel/runtime 7.8.4
@babel/core 7.8.4
@babel/plugin-transform-runtime 7.8.3
@babel/preset-env 7.8.4
@babel/register 7.8.3"

Directory Structure

my-app
├── .node_modules
├── src
│   ├── lib
│   │    └── seed_database.js
│   ├── v1
│   │    └── routes.js
│   ├── start.js
│   └── server.js
├── .babelrc
├── package-lock.json
├── package.json

start.js

require("@babel/register")({
    presets: [
      ["@babel/preset-env", {
        "targets": {
          "node": "current"
        }
      }]
    ]
});

module.exports = require('./server.js')

server.js

import express from 'express';
import v1ApiRoutes from './v1/routes';
import constants from './config/constants';

const app = express();
app.use('/v1', v1ApiRoutes);

app.listen(constants.PORT, err => {
    if (err) {
        console.log('Cannot run!')
    } else {
        console.log(`App listening on port: ${constants.PORT}`)
    }
});

seed_database.js

const db = require('../../config/db')['appDb'];

...

db.js

...

export const appDb = appDb;

.babelrc

{
    "plugins": [
        ["@babel/transform-runtime"]
    ]  
}

Update

Jeremy Harris' suggestion works:

require("@babel/register")({
    presets: [
      ["@babel/preset-env", {
        "targets": {
          "node": "current"
        }
      }]
    ]
});

const db = require('../../config/db')['appDb'];

However, when we replace the require line with named imports:

import { appDb as db } from '../../config/db';

we now get a new error

SyntaxError: Cannot use import statement outside a module

Update #2

Using Jeremy Harris' second suggestion of a single entry point works

node start.js seed

start.js

require("@babel/register")({
    presets: [
      ["@babel/preset-env", {
        "targets": {
          "node": "current"
        }
      }]
    ]
});


if (process.argv.indexOf('seed') > -1) {
  module.exports = require('./lib/seed_database.js')
  return
}

 module.exports = require('./server.js')

@JeremyHarris That works! However, only works if I use const db = require(...). If we were to use named imports, such as import { appDb as db } from '../../config/db';, then we now get the error SyntaxError: Cannot use import statement outside a module — Nyxynyx
Maybe in start.js, you check for CLI args and if the argument is "seed" then you include the seeder, otherwise the normal server. That way it's only a single entry point for including babel. — Jeremy Harris
@JeremyHarris Thanks, now it works! Updated question with the code that works. Is the code written correctly? I find it strange to have 2 module.exports and a return after the first module.exports — Nyxynyx
Btw, should the require("@babel/register") line also appear in .bashrc? — Nyxynyx

Jeremy Harris Jeremy Harris · Accepted Answer · 2020-02-05T16:22:19

As we discussed in the comments, the issue is that your seed file was not including the @babel/register code, hence it didn't transpile it. Per the suggestion with CLI args, you could modify it to use a single module.exports like:

// Default module
let commandModule = './server.js';

// Override with different command
if (process.argv.indexOf('seed') > -1) {
  commandModule = './lib/seed_database.js';
}

module.exports = require(commandModule);

If you want to keep configuration in .babelrc, you can do this when including @babel/register:

require('@babel/register')({
  extends: './.babelrc',
  ignore: [/node_modules/],
});

This GitHub issue discusses some of the issues around it in case you run into any: https://github.com/babel/babel/issues/8321

Babel Not Working Outside of Main Node.js App

Update

Update #2

1 Answers