app.mjs

'use latest';

import express from 'express';
import compression from 'compression';

const app = express();

if (process.env.NODE_ENV === 'production') {
  app.use(compression());
}

app.get('*', (req, res) => {
  res.send('Hello world');
});

export default app;

bundle-mjs-test.mjs

'use latest';

import WT from 'webtask-tools';
import app from './app.mjs';

// export default doesn't work, import above works though
module.exports = WT.fromExpress(app);

package.json

{
  "name": "bundle-mjs-test",
  "version": "1.0.0",
  "description": "mjs bundle webtask test",
  "main": "bundle-mjs-test.mjs",
  "scripts": {
    "deploy": "wt create bundle-mjs-test.mjs --bundle --prod"
  },
  "license": "ISC",
  "dependencies": {
    "compression": "^1.7.0",
    "express": "^4.15.4",
    "webtask-tools": "^3.2.0"
  }
}