javascript : module

// key.js

export const birthKey = Symbol('Date of birth');
export const emailKey = Symbol('Emails');

// youjun.js

import { birthKey, emailKey } from './key';

export default {
  firstName: 'youjun',
  lastName: 'park',
  age: 22,
  [birthKey]: new Date(1985, 11, 16, 17, 30),
  [emailKey]: ['thiehis@gmail.com'],
};

// main.js

import youjun from './youjun.js';
import { birthKey, emailKey } from './key.js';

console.log(youjun);

console.log(Object.keys(youjun)); // ['firstName', 'lastName', 'age']

console.log(youjun[birthKey]);
console.log(youjun[emailKey]);

import { increase as increase1 } from './counter.js';
import { increase, getCount } from './counter.js';
import * as counter from './counter.js'; // This way you can import them as a group.

import increase  from './counter.js';

counter.increase();
counter.increase();
counter.increase();
console.log(counter.getCount());