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Question

I am trying to write a custom middleware to log a user into my application. For this I am using the below function:

async function login(username, password) {
    try {
        const pwdHash = await bcrypt.hash(password, saltRounds)
        const res = await knex("users").where({
            username: username,
            password: pwdHash
        }).first()
        console.log("res: " + res) //here I am getting the error
        if (res.password == pwdHash) {
            return true
        } else {
            return false
        }
    } catch (e) {
        console.log(e)
    }
}

However, I am getting the following error message back:

TypeError: Cannot read property '0' of undefined
    at Object.login (C:\Users\user\project\service\user.js:56:34)
    at <anonymous>

I know that I cannot access the res object immediately, but shouldn t await get an object back. However, I am getting get an object back. However, I am getting undefined` back.

Any suggestions what I am doing wrong?

Appreciate your replies!

Answer 1

I found this, https://github.com/mysqljs/mysql/issues/910#issuecomment-55536265 .

what I think is happening here is that your query is returning an empty array and the .first() method is doing something with the [0] item which is undefined in that case, so that's why you are getting that error Cannot read property '0' of undefined .

You can improve your code doing something like this:

async function login(username, password) {
    try {
        const pwdHash = await bcrypt.hash(password, saltRounds)
        const res = await knex("users").where({
            username: username,
            password: pwdHash
        });
        // res should be an empty array here if there is no match

        // Just check if the query gives you some result
        // so, if the array has some item inside then it means 
        // that you found a valid user with that `username` and `password`
        if (res.length > 0) {
            return true
        } else {
            return false
        }
    } catch (e) {
        console.log(e)
    }
}