0

I have a signup user function that I dont really understand how it's working...

module.exports.signupUser = async (req, res) => {
let email = req.body.email;
let password = req.body.password;
if(!validator.isEmail(email))
{
    res.status(400).json({
        "message": "Please enter a valid email!"
    }).end();
}
else if(!validator.isLength(password, {min:6})){
    res.status(400).json({
        "message": "Password must have at least 6 characters!"
    }).end();
}
else {
    const salt = bcrypt.genSaltSync(10);
    const hashedPassword = await bcrypt.hash(password, salt);
    let params = [email, hashedPassword];
    console.log(hashedPassword);

    let query = 'insert into users (email, password) values (?,?)';
    connection.query(query, params, (err, result, fields) => {
        if(err && err.code === 'ER_DUP_ENTRY') {
            res.status(400).json({
                "message": "There is an account already associated with this email adress!"
            }).end();
        }
        else {
            res.status(200).json({
                "message": "User created!"
            }).end();
        }
    });
}

}

So in the last else, I use await bcrypt.hash(password, salt) to encrypt my password. I'm new to JS but still I understand that await executes code asyncronously, so console.log(hashedPassword) should not return me the hashed password because this log will execute before the actual hashing. Anyone can explain me what is really happening?

Jigau Rafael
  • 1
  • `I understand that await executes code asyncronously`...no. await causes your application to wait for code which would otherwise be asynchronous to complete, before continuing to the next line. Without it, the async code would run at the same time as the lines following it. I think you've just got your understanding backwards – ADyson Sep 29 '21 at 16:07
  • Some documentation for this? Really trying to understand but still seems like i got it very badly... thanks! – Jigau Rafael Sep 29 '21 at 16:12
  • So if I wouldnt use the await keyword, the log would be some pending promise, but using it would actually stop the code at that line and wait for the result... – Jigau Rafael Sep 29 '21 at 16:17
  • `await` pauses the execution of the `function` until the result it is `await` for is resolved. – Sachin Ananthakumar Sep 29 '21 at 16:28
  • MDN documentation is quite good to understand basic javascript paradigm. Have a look for await here https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Operators/await and have a look for asynchronicity with Promises here https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Global_Objects/Promise. – Bloodbee Sep 29 '21 at 16:34
  • `So if I wouldnt use the await keyword, the log would be some pending promise, but using it would actually stop the code at that line and wait for the result.`... yeah that's pretty much right, but it's not the log which is pending, it's the hash() function which is pending (since that's the thing you were awaiting). So that runs in the background and meanwhile the rest of your code continues at the same time – ADyson Sep 29 '21 at 17:10
  • thanks for all the responses! – Jigau Rafael Sep 29 '21 at 17:55

2 Answers2

1
const hashedPassword = await bcrypt.hash(password, salt);
console.log(hashedPassword);

If you use the await keyword, nodejs will wait for promise to resolve before moving to the next line in the async function. Your console.log's result will be the hashed password.

If you don't use the await keyword, node will start resolving the promise but will not wait for it to finish resolving before moving to next line. Your console.log's result will be Promise { pending }

Muhammed Sabeeh
  • 185
  • 11
1

await executes the code synchronously. So in your case await will wait for the execution of bcrypt.hash.

For more clarity bcrypt.hash function returns a promise and now we have two choices here.

1. Await for the promise to resolve

const hashedPassword = await bcrypt.hash(password, salt);
console.log(hashedPassword);

the hashedPassword will contain the actual output we need.

2. Handle promise resolution using then

bcrypt.hash(password, salt).then(hashedPassword => {
    console.log(hashedPassword);
})

As the bcrypt.hash function returns a promise, we need to handle the rest of the code inside a then block as it'll only return the value once the function resolves the promise.

In case you want to execute your code asynchronously, you need to remove the await keyword which waits for the promise to resolve before moving to the next line.

Rajendrasinh Parmar
  • 487
  • 6
  • 17