When you are using ECMAScript modules you are forced to provide the file extension: https://nodejs.org/api/esm.html#esm_mandatory_file_extensions
So, on top of what other suggested of using "type": "module" on package.json you also need to specify the file extension import {urls} from './helpers.js'.
You can also use the flag --es-module-specifier-resolution=node to make it resolve js files as modules just like it did before with require