Transpile Turbo/Rails Turbo for IE 11 - ruby-on-rails

Question

I have a rails app using Hotwire (Turbo & Stimulus). I'm trying to use webpack and babel to transpile JS for ES5/IE11. Stimulus and Turbo don't support IE11 any more, so I'm also trying to explicitly transpile them and then add required polyfills. My understanding is even if they've already been transpiled, the result should still be valid ES6 that can be transpiled again.
For Stimulus this approach appears to work fine but for Turbo I get
Uncaught TypeError: t.tagName is undefined
ht turbo.es2017-esm.js:1308
My best guess is that this is because Turbo is distributed as UMD modules so my babel config isn't transpiling it correctly. What's the best way to approach this?
browserlist:
"browserslist": {
"production": [
"last 1 version",
"> 1%",
"IE 10"
],
webpack.config.js:
const path = require("path")
const webpack = require("webpack")
const MiniCssExtractPlugin = require('mini-css-extract-plugin')
const RemoveEmptyScriptsPlugin = require('webpack-remove-empty-scripts')
const CopyPlugin = require("copy-webpack-plugin");
const mode = process.env.NODE_ENV === 'development' ? 'development' : 'production'
module.exports = {
mode,
devtool: "source-map",
entry: {
application: [
"./app/frontend/application.js",
]
},
module: {
rules: [
{
test: /\.(js|ts)$/,
include: [
path.resolve(__dirname, 'node_modules/#hotwired/turbo'),
path.resolve(__dirname, 'node_modules/#hotwired/turbo-rails'),
path.resolve(__dirname, 'node_modules/#hotwired/stimulus'),
path.resolve(__dirname, 'node_modules/#stimulus/polyfills'),
path.resolve(__dirname, 'node_modules/#rails/actioncable'),
path.resolve(__dirname, 'app/frontend'),
],
use: ['babel-loader'],
},
{
test: /\.(png|jpe?g|gif|eot|woff|woff2|ttf|svg|ico)$/i,
type: 'asset/resource'
},
{
test: /\.(scss|css)/i,
use: [MiniCssExtractPlugin.loader, 'css-loader', 'sass-loader'],
}
],
},
resolve: {
modules: ['node_modules']
},
output: {
filename: "[name].js",
// we must set publicPath to an empty value to override the default of
// auto which doesn't work in IE11
publicPath: '',
path: path.resolve(__dirname, "app/assets/builds"),
},
plugins: [
new RemoveEmptyScriptsPlugin(),
new MiniCssExtractPlugin(),
new webpack.optimize.LimitChunkCountPlugin({ maxChunks: 1 }),
new CopyPlugin({
patterns: [
{ from: "node_modules/html5shiv/dist/html5shiv.min.js", to: "vendor" },
{ from: "app/frontend/vendor/outerHTML.js", to: "vendor" },
{ from: "app/frontend/vendor/polyfill-output-value.js", to: "vendor" }
],
}),
new webpack.ProvidePlugin({
$: 'jquery',
jQuery: 'jquery',
jquery: 'jquery',
'window.jQuery': 'jquery'
})
]
}
babel.config.js
module.exports = function(api) {
var validEnv = ['development', 'test', 'production']
var currentEnv = api.env()
var isDevelopmentEnv = api.env('development')
var isProductionEnv = api.env('production')
var isTestEnv = api.env('test')
if (!validEnv.includes(currentEnv)) {
throw new Error(
'Please specify a valid `NODE_ENV` or ' +
'`BABEL_ENV` environment variables. Valid values are "development", ' +
'"test", and "production". Instead, received: ' +
JSON.stringify(currentEnv) +
'.'
)
}
return {
presets: [
isTestEnv && [
'#babel/preset-env'
],
(isProductionEnv || isDevelopmentEnv) && [
'#babel/preset-env',
{
forceAllTransforms: true,
useBuiltIns: 'entry',
corejs: '3.21.1',
modules: false,
exclude: ['transform-typeof-symbol']
}
]
].filter(Boolean),
plugins: [
'babel-plugin-macros',
'#babel/plugin-syntax-dynamic-import',
isTestEnv && 'babel-plugin-dynamic-import-node',
'#babel/plugin-proposal-class-properties',
'#babel/plugin-proposal-object-rest-spread',
'#babel/plugin-proposal-private-methods',
'#babel/plugin-proposal-private-property-in-object',
'#babel/plugin-transform-regenerator',
'#babel/plugin-transform-runtime',
[
'#babel/plugin-transform-spread',
{
loose: true
}
]
].filter(Boolean)
}
}