How to do it...

1. Create a new folder with an index.html file, as seen in Exporting/importing multiple modules for external use.
2. Inside of that directory, create a folder named rockets.
3. Inside of rockets, create three files: falcon-heavy.js, saturn-v.js, and launch-sequence.js:

// falcon-heavy.js 
import { launchSequence } from './launch-sequence.js'; 
 
export const name = "Falcon Heavy"; 
export const COUNT_DOWN_DURATION = 5; 
 
export function launch () { 
  launchSequence(COUNT_DOWN_DURATION, name); 
} (COUNT_DOWN_DURATION); 
} 
 
// saturn-v.js 
import { launchSequence } from './launch-sequence.js'; 
 
export const name = "Saturn V"; 
export const COUNT_DOWN_DURATION = 10; 
 
export function launch () { 
  launchSequence(COUNT_DOWN_DURATION, name); 
} 
 
// launch-sequence.js 
export function launchSequence (countDownDuration, name) { 
  let currCount = countDownDuration; 
  console.log(`Launching in ${COUNT_DOWN_DURATION}`, name); 
 
  const countDownInterval = setInterval(function () { 
    currCount--; 
 
    if (0 < currCount) { 
      console.log(currCount); 
    } else { 
      console.log('%s LIFTOFF!!! ', name); 
      clearInterval(countDownInterval); 
    } 
  }, 1000); 
} 

4. Now create index.js, which exports the members of those files:

import * as falconHeavy from './falcon-heavy.js'; 
import * as saturnV from './saturn-v.js'; 
export { falconHeavy, saturnV }; 

5. Create a main.js file (in the folder that contains rockets), which imports falconHeavey and saturnV from the index.js file and launches them:

import { falconHeavy, saturnV } from './rockets/index.js' 
 
export function main () { 
  saturnV.launch(); 
  falconHeavy.launch(); 
} 

6. Open in the browser, and see the following output: