Given that the module from the Defining a Module section exists in the file test.js, you can import from that module and use its exported members:
import {doSomething, MyClass, PI} from './test'
doSomething()
const mine = new MyClass()
mine.test()
console.log(PI)
The somethingPrivate() method was not exported from the test module, so attempting to import it will fail:
import {somethingPrivate} from './test'
somethingPrivate()