[Build] revert site to webpack config (#3747)

docs/site/utils/index.js

@@ -0,0 +1,33 @@
+function iframeReady(iframe, callback) {
+  const doc = iframe.contentDocument || iframe.contentWindow.document;
+  const interval = () => {
+    if (iframe.contentWindow.changePath) {
+      callback();
+    } else {
+      setTimeout(() => {
+        interval();
+      }, 50);
+    }
+  };
+
+  if (doc.readyState === 'complete') {
+    interval();
+  } else {
+    iframe.onload = interval;
+  }
+}
+
+const ua = navigator.userAgent.toLowerCase();
+const isMobile = /ios|iphone|ipod|ipad|android/.test(ua);
+
+function importAll(map, r) {
+  r.keys().forEach(key => {
+    map[key] = r(key);
+  });
+}
+
+export {
+  isMobile,
+  importAll,
+  iframeReady
+};