初始化项目，添加sum函数和package.json文件

index.js

@@ -0,0 +1,3 @@
+export function sum(a, b) {
+  return a + b;
+}

package.json

@@ -0,0 +1,12 @@
+{
+  "name": "utils",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC"
+}