Use babel to transform JS

After this, we can generally use most modern JS
without having to look at caniuse.com and see if
the feature is supported.

Ref #1373

Author: yuvipanda

babel.config.json

@@ -0,0 +1,3 @@
+{
+  "presets": ["@babel/preset-env"]
+}

package.json

@@ -3,6 +3,10 @@
   "version": "0.1.0",
   "description": "`BinderHub`",
   "devDependencies": {
+    "@babel/cli": "^7.15.7",
+    "@babel/core": "^7.15.5",
+    "@babel/preset-env": "^7.15.6",
+    "babel-loader": "^8.2.2",
     "css-loader": "^6.2.0",
     "eslint": "^7.32.0",
     "mini-css-extract-plugin": "^2.3.0",
@@ -12,8 +16,8 @@
   "dependencies": {
     "bootstrap": "^3.4.0",
     "clipboard": "^2.0.8",
-    "jquery": "^3.6.0",
     "event-source-polyfill": "^1.0.25",
+    "jquery": "^3.6.0",
     "xterm": "^4.14.1",
     "xterm-addon-fit": "^0.5.0"
   },

webpack.config.js

@@ -23,6 +23,16 @@ module.exports = {
     ],
     module: {
         rules: [
+            {
+                test: /\.js$/,
+                exclude: /(node_modules|bower_components)/,
+                use: {
+                  loader: 'babel-loader',
+                  options: {
+                    presets: ['@babel/preset-env'],
+                  }
+                }
+            },
             {
                 test: /\.css$/i,
                 use: [