Question

我正在建立一个社交网络来学习nodejs和reactjs。当前，在用邮递员在/signin调试中构建后端时，我什至无法启动节点服务器，该cmd会引发以下错误：

\node_react\2\nodeapi\controllers\auth.js:40
const {_id, name, email} = user;
          ^
SyntaxError: Identifier 'email' has already been declared

引发错误的代码段如下：

//generate a token with user id and secret
const token = jwt.sign({_id: user._id}, process.env.JWT_SECRET);

//persist the token as 't' in cookie with expiry date
res.cookie("t", token, {expire: new Date() + 9999});

//return response with user and token to frontend client
const {_id, name, email} = user;
return res.json({token, user:{_id, email, name}});

完整的auth.js代码如下：

const jwt = require("jsonwebtoken");
require ('dotenv').config();
const User = require("../models/user");

exports.signup = async (req, res) => {
    const userExists = await User.findOne({email: req.body.email});
    if(userExists) 
        return res.status(403).json({
            error: "Email is taken!"
        }); 
    const user = await new User(req.body);
    await user.save();
    res.status(200).json({ message: "Signup success! Please login:)" });
};

exports.signin = (req,res) => {
    //find the user based on email
    const { email, password } = req.body 
    User.findOne({email}, (err, user) => {
        //if error or no user
        if (err || !user) {
            return res.status(401).json({
                error: "User with that email does not exists. Please signin."
            });
        }
        //if user is found make sure the email and password match
        // create authenticate method in model and use here
        if (!user.authenticate(password))
            return res.status(401).json({
                error: "Email and password do not match."
            });
    })

    //generate a token with user id and secret
    const token = jwt.sign({_id: user._id}, process.env.JWT_SECRET);

    //persist the token as 't' in cookie with expiry date
    res.cookie("t", token, {expire: new Date() + "9999"});
    //return response with user and token to frontend client
    const {_id, name, email} = user;
    return res.json({token, user:{_id, email, name}});      
}

Answer 1

const {_id, name, email} = user;被称为解构，它将为新变量分配与对象相同的名称。

所以这个：

const {_id, name, email} = user;

与：

const _id = user._id;
const name = user.name;
const email = user.email;

也就是说，您可能在重新定义email变量，该变量是用const关键字设置的。这意味着您无法重新分配它。

您可以做的是：

const {_id, name, email: _email} = user;
return res.json({token, user:{_id, name, email: _email}});

这将使email字段分配给_email变量，从而避免冲突。

Answer 2

在您的代码中，您将覆盖email变量，该变量是使用const关键字创建的（又名：无法重新分配）。

Jeena的答案可能解决了问题，但看来您有更深的问题。

User.findOne({email}, (err, user){}是异步的。因此，此代码下的代码可能会失败。

您可能必须将代码重写为：

exports.signin = (req,res) => {
    //find the user based on email
    const { email, password } = req.body 
    User.findOne({email}, (err, user) => {
        //if error or no user
        if (err || !user) {
            return res.status(401).json({
                error: "User with that email does not exists. Please signin."
            });
        }
        //if user is found make sure the email and password match
        // create authenticate method in model and use here
        if (!user.authenticate(password))
            return res.status(401).json({
                error: "Email and password do not match."
            });

        //generate a token with user id and secret
        const token = jwt.sign({_id: user._id}, process.env.JWT_SECRET);

        //persist the token as 't' in cookie with expiry date
        res.cookie("t", token, {expire: new Date() + "9999"});
        //return response with user and token to frontend client
        const {_id, name, email} = user;
        return res.json({token, user:{_id, email, name}});      
    })
}

cookies和response必须在MongoDB查询中，因此您确实拥有用户。

标识符…已经被声明

2 个答案: