Express4 index.js cannot find custom module

  node.js, question

With the framework of express4, there is no problem with the custom module. I can use it normally when calling with other js files, but when requesting in index.js,
var userDao = require(“./dao/userDao”);
Error: cannotfindmodule’./Dao/userdao’ is displayed
What is the problem?

./index.js
./dao/userDao.js

Are you sure your relative path is not wrong?