Webpack + babel are basically rewriting `import` and `require` calls into their own `__webpack_require__` helper and converting ESM to CJS. Whereas `require` an

Webpack + babel are basically rewriting `import` and `require` calls into their own `__webpack_require__` helper and converting ESM to CJS. Whereas `require` and `import` are node built-ins and `import` is browser built-in. Making stuff interoperate requires some trickery and lax spec compliance. There are high chances you are relying on some non-spec compliant behaviors but you don't know about it. For example, ESM exports have immutable bindings, which means, mocking exports for unit testing is impossible. If it works for you, it's because you transpile the code from ESM to CJS (either via `babel`, `rewire` or similar tool).