我正在创建一个登录-注销演示

Question

when i am posting to my register route i am using following code to check the user in database but my destructor is showing user as undefined but i have defined the user

    updateUser(userDetails){
        User.find({}, function (err, foundItems){
            console.log(foundItems[0].email)
            const checkUserByEmail = foundItems.find((u)=> u.email === userDetails.email)
            console.log(checkUserByEmail)
            if(checkUserByEmail){
                console.log("adsakhdsk")
                return {
                    error : "user already exist"
                }
            }
            const user = new User({
                email : userDetails.email,
                password: userDetails.password
            })
            user.save()
            return {
                user : userDetails
            }
            })
        }
    }

this is my register method to register a user

  register = (req, res) => {
    const userDetails = {
      email: req.body.email,
      password: req.body.password,
    }
    const { user , error } = usersdb.updateUser(userDetails)
    console.log([user , error])
}

the error i am getting

TypeError: Cannot destructure property 'user' of 'usersdb.updateUser(...)' as it is undefined.
    at register (C:\Users\USER\Desktop\nodejs\login-logut-demo\api\auth\router.js:13:13)
    at Layer.handle [as handle_request] (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\layer.js:95:5)
    at next (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\route.js:137:13)
    at Route.dispatch (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\layer.js:95:5)
    at C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\index.js:281:22
    at Function.process_params (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\index.js:335:12)
    at next (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\index.js:275:10)
    at Function.handle (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\index.js:174:3)
    at router (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\index.js:47:12)
    at Layer.handle [as handle_request] (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\layer.js:95:5)
    at trim_prefix (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\index.js:317:13)
    at C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\index.js:284:7
    at Function.process_params (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\index.js:335:12)
    at next (C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\express\lib\router\index.js:275:10)
    at C:\Users\USER\Desktop\nodejs\login-logut-demo\node_modules\body-parser\lib\read.js:130:5

Answer 1

Database requests are asynchronous. What I suspect might be happening in your case is you try to read the value of 'user' before the updateUser method is done retrieving the data from the DB.

I suggest you to look into nodeJS promises & the await async syntax

updateUser(userDetails){
    return new Promise((resolve, reject) => {
        User.find({}, function (err, foundItems) {
            console.log(foundItems[0].email)
            const checkUserByEmail = foundItems.find((u) => u.email === userDetails.email)
            console.log(checkUserByEmail)
            if (checkUserByEmail) {
                console.log("adsakhdsk")
                resolve({
                    error: "user already exist"
                })
            }
            const user = new User({
                email: userDetails.email,
                password: userDetails.password
            })
            user.save()
            resolve({
                user: userDetails
            })
        })
    })
}


register = async (req, res) => {
    const userDetails = {
        email: req.body.email,
        password: req.body.password,
    }
    const { user, error } = await usersdb.updateUser(userDetails)
    console.log([user, error])
}

This is a possible solution to your error

What happens here is that the updateUser method now returns a Promise that can be handled using async/await.

Basically it enables us to tell the program, hey wait till this block of code finishes execution. The promise ends when u call resolve() , and it throws an exception with reject()

The returned data by the asynchronous function is sent as the parameter for the resolve() callback.