How to retrieve the file where an error occurred?

I'm trying to retrieve the file where an error occurred and all I'm able to catch is a standard JavaScript error with a message but not file.

For example:

> index.js

```javascript
const mdeps = require('module-deps');
const md = mdeps();

md.on('error', (e) => {
console.warn(e);
});
md.end({ file:'./main.js' });
```
> main.js

```javascript
require('./partial'); // ./partial exists

require('unknown'); // unknown doesn't
```

The error thrown is:

> Error: Cannot find module 'unknown' from '/home/ericmorand/Projects/module-deps-test'

Except by parsing the error message, which is not a serious option - and even this way I would not be able to get the file name, I can't find a way to retrieve the file where the error happened.

I thought that I would be able to catch the correct file by registering to the `file` event like this:

```javascript
const mdeps = require('module-deps');
const md = mdeps();

let currentFile;

md.on('file', (file) => {
currentFile = file;
});
md.on('error', (e) => {
console.warn(currentFile); // will print ./partial

console.warn(e);
});
md.end({ file:'./main.js' });
```

But the `currentFile` contains `./partial.js` because it is the latest file encountered successfully by module-deps. And it is not where the error happens.

Can someone point me to the solution?