```
const express = require('express');
const app = express();
app.use(express.json());
app.get('/', (req, res) => {
 const data = {'message': 'Hello World!'}
 res.send(data);
});
app.listen(3000, () => {
 console.log('Listening on 3000');
});
```

This is an example Express server that listens for requests on port 3000 and responds with a JSON object containing the message "Hello World!". You can test it by opening your web browser and going to `http://localhost:3000`.