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()