the thing with webpack is that the classes you have created are properly encapsulated from the outside world. the error you are getting

warning: react.createelement: type should not be null, undefined, boolean, or number. 
it should be a string (for dom elements) or a reactclass (for composite components).

is an error with react when react cannot find the class declaration anywhere. while i would suggest you follow the proper way and instantiate it in an index.jsx file, you can still make that work by doing this hack in dropdown.jsx

window.dropdown = dropdown

this would make sure that your external non webpack compiled javascript can see the dropdown class. but this is bad pactice and i would really suggest you stick with the index.jsx file as it protects you from exposing your classes and libraries from the global namespace and its a best practice.

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