Does not detect class extend from module without file extension #160

This does not work:

import DataSource from './DataSource';

class ArrayDataSource extends DataSource {}

It does not detect that ArrayDataSource extends from DataSource. The documentation lists it as "src/ArrayDataSource.js~DataSource".

If I include the file extension of DataSource.js it works.

import DataSource from './DataSource.js';

class ArrayDataSource extends DataSource {}

I think both imports should work the same way, as they do in Node, Browserify, etc. Perhaps use require.resolve internally to resolve the filename of imports?