pokemon.trade/config/webpack/environment.js

const {environment} = require('@rails/webpacker');
const PnpWebpackPlugin = require('pnp-webpack-plugin');

const babelLoader = environment.loaders.get('babel');
babelLoader.test = /\.(ts|tsx|js|jsx|mjs)?(\.erb)?$/;
babelLoader.use.push({
  loader: 'ts-loader',
  options: PnpWebpackPlugin.tsLoaderOptions(),
});

module.exports = environment;