diff --git a/src/data/index.js b/src/data/index.js
new file mode 100644
index 0000000..e926992
--- /dev/null
+++ b/src/data/index.js
@@ -0,0 +1,12 @@
+class Singleton {
+  static getInstance() {
+    if (!Singleton.instance) {
+      Singleton.instance = new Singleton();
+    }
+    return Singleton.instance;
+  }
+}
+
+const s1 = Singleton.getInstance();
+const s2 = Singleton.getInstance();
+console.log(s1 === s2); // true
diff --git a/src/flow/index.js b/src/flow/index.js
new file mode 100644
index 0000000..8e27aed
--- /dev/null
+++ b/src/flow/index.js
@@ -0,0 +1,3 @@
+class Flow {}
+
+module.exports = new Flow();
diff --git a/src/service/AccountService.js b/src/service/AccountService.js
new file mode 100644
index 0000000..1d4668a
--- /dev/null
+++ b/src/service/AccountService.js
@@ -0,0 +1,3 @@
+class AccountService {}
+
+module.exports = new AccountService();