Use rollup to bundle JS, run babel through rollup

.eslintrc.json

@@ -12,5 +12,8 @@
         "quotes": ["error", "single"],
         "semi": ["error", "always"],
         "compat/compat": "error"
+    },
+    "parserOptions": {
+        "sourceType": "module"
     }
 }

.rollup.config.js

@@ -0,0 +1,19 @@
+import resolve from 'rollup-plugin-node-resolve';
+import commonjs from 'rollup-plugin-commonjs';
+import babel from 'rollup-plugin-babel';
+
+export default {
+    input: 'src/scripts/index.js',
+    output: {
+        file: 'src/js/main.js',
+        format: 'iife',
+        sourcemap: true,
+    },
+    plugins: [
+        resolve(),
+        commonjs(),
+        babel({
+            exclude: ['node_modules/**'],
+        }),
+    ],
+};