Node.js登录脚本报错：Cannot read properties of undefined (reading 'findOne')

问题场景 #

开发Node.js网页登录页面，已完成MongoDB后台配置且登录账户已存入数据库，但登录时触发如下错误：

var User = await User.findOne({
TypeError: Cannot read properties of undefined (reading 'findOne')
    at C:\Users\Mmart\Desktop\twitter\routes\loginRoutes.js:20:39
    at Layer.handle [as handle_request] (C:\Users\Mmart\Desktop\twitter\node_modules\express\lib\router\layer.js:95:5)
    at next (C:\Users\Mmart\Desktop\twitter\node_modules\express\lib\router\route.js:144:13)
    at Route.dispatch (C:\Users\Mmart\Desktop\twitter\node_modules\express\lib\router\route.js:114:3)
    at Layer.handle [as handle_request] (C:\Users\Mmart\Desktop\twitter\node_modules\express\lib\router\layer.js:95:5)
    at C:\Users\Mmart\Desktop\twitter\node_modules\express\lib\router\index.js:284:15
    at Function.process_params (C:\Users\Mmart\Desktop\twitter\node_modules\express\lib\router\index.js:346:12)
    at next (C:\Users\Mmart\Desktop\twitter\node_modules\express\lib\router\index.js:280:10)
    at Function.handle (C:\Users\Mmart\Desktop\twitter\node_modules\express\lib\router\index.js:175:3)
    at router (C:\Users\Mmart\Desktop\twitter\node_modules\express\lib\router\index.js:47:12)

对应登录脚本代码：

router.post("/", async(req,res,next) => {

        var payload = req.body;

        if(req.body.logUsername && req.body.logPassword){
                var User = await User.findOne({
                        $or: [
                                { username: logUsername },
                                { email: logUsername }
                        ]
                })
                .catch((error) => {
                        console.log(error);
                        payload.errorMessage = "something went wrong.";
                        res.status(200).render("login", payload);
                });
                if (user != null){
                        var result = bcrypt.compare(req.body.logPassword,user.Password);

                        if(result === true){
                                req.session.user = user;
                                return res.redirect("/");
                        }
                }
                payload.errorMessage = "login creds wrong.";
                return res.status(200).render("login", payload);
        }
        payload.errorMessage = "check values";
        res.status(200).render("login");
})

错误原因与解决办法 #

1. 变量命名冲突（核心错误） #

代码中用var User = await User.findOne(...)，当前作用域的User变量覆盖了外部导入的Mongoose模型User。由于await是异步操作，执行到User.findOne时，当前作用域的User还未赋值，导致调用findOne时User为undefined，触发报错。

解决：
将查询结果变量名改为小写user（或其他不冲突名称）：

var user = await User.findOne({
    $or: [
        { username: req.body.logUsername },
        { email: req.body.logUsername }
    ]
})

2. 未定义变量logUsername #

代码中直接使用logUsername但未声明，该变量需从req.body中获取。

解决：
提前声明变量或直接使用req.body.logUsername：

const logUsername = req.body.logUsername;
// 或直接在查询条件中写req.body.logUsername

3. bcrypt.compare是异步函数 #

bcrypt.compare返回Promise对象，直接用=== true判断会得到false，因为Promise不等于布尔值true。

解决：
用await等待异步结果：

var result = await bcrypt.compare(req.body.logPassword, user.password);
// 注意：确保user.password与Mongoose模型中定义的密码字段大小写一致

4. 变量大小写不一致 #

代码中查询结果用小写user，但后续判断if (user != null)时，若前面变量名错误会导致user未定义；同时注意数据库中密码字段的大小写（比如user.Password vs user.password），必须与模型定义一致。

5. 确认模型导入 #

确保在loginRoutes.js顶部正确导入User模型：

const User = require('../models/User'); // 根据实际文件路径调整

修正后的完整代码示例 #

const bcrypt = require('bcrypt');
const User = require('../models/User'); // 确认模型路径正确

router.post("/", async(req,res,next) => {
    var payload = { ...req.body };

    if(req.body.logUsername && req.body.logPassword){
        try {
            const logUsername = req.body.logUsername;
            const user = await User.findOne({
                $or: [
                    { username: logUsername },
                    { email: logUsername }
                ]
            });

            if (user != null){
                const result = await bcrypt.compare(req.body.logPassword, user.password);

                if(result){
                    req.session.user = user;
                    return res.redirect("/");
                }
            }
            payload.errorMessage = "登录凭据错误。";
        } catch (error) {
            console.log(error);
            payload.errorMessage = "服务器出错，请稍后重试。";
        }
        return res.status(200).render("login", payload);
    }
    payload.errorMessage = "请填写完整的用户名/邮箱和密码。";
    res.status(200).render("login", payload);
})

内容的提问来源于stack exchange，提问作者Mitchell