Rewrite frontend using create-react-app

client/DOMUtils.js

@@ -0,0 +1,15 @@
+export const addEvent = (node, type, handler) => {
+  if (node.addEventListener) {
+    node.addEventListener(type, handler, false)
+  } else if (node.attachEvent) {
+    node.attachEvent('on' + type, handler)
+  }
+}
+
+export const removeEvent = (node, type, handler) => {
+  if (node.removeEventListener) {
+    node.removeEventListener(type, handler, false)
+  } else if (node.detachEvent) {
+    node.detachEvent('on' + type, handler)
+  }
+}