Upgrade to Webpacker 6.0.

config/webpack/base.js

@@ -0,0 +1,25 @@
+const { webpackConfig, merge } = require('@rails/webpacker')
+
+module.exports = merge(webpackConfig, {
+  output: {
+    library: "Danbooru",
+  },
+  resolve: {
+    alias: {
+      "jquery": "jquery/src/jquery.js",
+      "react": "preact/compat",
+      "react-dom": "preact/compat",
+    }
+  },
+  module: {
+    rules: [{
+      test: /.erb$/,
+      enforce: "pre",
+      exclude: /node_modules/,
+      loader: "rails-erb-loader",
+      options: {
+        runner: "bin/rails runner"
+      }
+    }]
+  },
+});