Import a regular javascript file with webpack

An NPM module offer some extensions in a folder :

gojs
   extensions
       DebugInspector.js
   release
   packages.json

Each extensions contain one class without any (es2015) export syntax like :

function Inspector(...) {

}

Inspector.prototype.inspectObject = function(obj) {

}

How to use it with webpack ? I tried a simple export like :

import 'gojs/extensions/DebugInspector.js';

The file is correctly imported and compiled but I can't create a new instance of DebugInspector, the Inspector function is undefined. It's probably, surely a duplicate question but I can't find any example like this code (or I dont use the correct words to search).

This example is not related to the Mike's example because the imported file doesn't support any AMD mechanism.