If you require moment.js in your client-side code webpack will put all of moment.js's locale files into your bundle (over 90 different locales). This causes a significant bundle increase and it's usually unnecessary.
To avoid it, a require to moment.js will only load moment.js without any locales. If you need to have some of its locales, you can require them yourself like that:
const moment = require('moment');
require('moment/locale/ja');
moment.locale('ja');
...You can read more about it here: https://github.com/jmblog/how-to-optimize-momentjs-with-webpack/blob/master/README.md