我有两个文件夹，中间件和路由。Routes包含一个route.js文件，其中包含：

const { verifySignUp } = require("../middlewares");
    module.exports = function(app) {
    app.use(function(req, res, next) {
    res.header(
      "Access-Control-Allow-Headers",
      "x-access-token, Origin, Content-Type, Accept"
    );
    next();
    });

    app.post(
    "/api/auth/signup",
    [
      verifySignUp.checkDuplicateUsernameOrEmail,
      verifySignUp.checkRolesExisted
    ],
    controller.signup
    );

    app.post("/api/auth/signin", controller.signin);
    };

verifySignUp.js包含：

checkDuplicateUsernameOrEmail = (req, res, next) => {...}

当我尝试调用checkDuplicateUsernameOrEmail函数时，它返回错误
TypeError: Cannot read property 'checkDuplicateUsernameOrEmail' of undefined
我不明白。我做错了什么？