在 NodeJS 中抛出错误 - UnhandledPromiseRejection

Question

I'm pretty new on NodeJS and I'm still trying to figure out how to handle errors. I read a lot of questions but I don't realize what I'm doing wrong.

Here I have a login function:

export const login = async (req, res) => {
let body = req.body;

try {
  const user = await User.findOne({ username: body.username });

if (!user) {
  throw new InternalError("Username or password are wrong");
}

if (!bcrypt.compareSync(body.password, user.password)) {
  throw new InternalError("Username or password are wrong");
}

let token = jwt.sign({ data: user }, "secret", {
  expiresIn: 60 * 60 * 24 * 30
});

return res.json({
  user: user,
  token: token
 });
} catch (error) {
throw new GenericError(error);
 }
};

And this is the error I get if, for example, I include a wrong password:

(node:12332) UnhandledPromiseRejectionWarning: GenericError: Username or password are wrong
(node:12332) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by 
throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch()

I know the promises made with Await must have a .then() and .catch() but this is not an error on executing the promise but on validating the password. What I want is to throw the error and get the response. Right now the request never ends and the previous error is displayed.

Thank you!

PS: InternalError and GenericError are just errors created by me which extends from Error

Answer 1

You receive the warning from node because you are re-throwing a GenericError after catching InternalError. Instead of re-throwing the GenericError, you should return your response or catch your GenericError when calling login .

Here is your code modified for both.

export const login = async (req, res) => {
  // We get the body info
  let body = req.body;

  try {
    // We find the user with the username from the body
    const user = await User.findOne({ username: body.username });

    // Let's assume no user exists, so we throw an InternalError,
    // This skips straight to the catch block.
    if (!user) {
      throw new InternalError("Username or password are wrong");
    }

    // We never reach these two statements
    // because of the error above being thrown.
    if (!bcrypt.compareSync(body.password, user.password)) {
      throw new InternalError("Username or password are wrong");
    }

    let token = jwt.sign({ data: user }, "secret", {
      expiresIn: 60 * 60 * 24 * 30
    });

   res.json({
      user: user,
      token: token
    });
  } catch (err) {
    // We caught our InternalError from not having a user above.
    // Now we should return a response that the user is invalid.
    // I am just going to return the error that we previously threw.
   res.json({
      error: err
    });
  }
};

You can definitely throw the GenericError from your catch block. However, doing that then requires you to catch the GenericError wherever you are calling your login function.

export const login = async (req, res) => {
  // We get the body info
  let body = req.body;

  try {
    // We find the user with the username from the body
    const user = await User.findOne({ username: body.username });

    // Let's assume no user exists, so we throw an InternalError,
    // This skips straight to the catch block.
    if (!user) {
      throw new InternalError("Username or password are wrong");
    }

    // We never reach these two statements
    // because of the error above being thrown.
    if (!bcrypt.compareSync(body.password, user.password)) {
      throw new InternalError("Username or password are wrong");
    }

    let token = jwt.sign({ data: user }, "secret", {
      expiresIn: 60 * 60 * 24 * 30
    });

   res.json({
      user: user,
      token: token
    });
  } catch (err) {
    // Throw the generic error
    throw GenericError(err);
  }
};


try {
  // We call the login function that is defined above.
  // It is going to throw a GenericError, so we have to
  // catch it.
  await login(req, res);
} catch (err) {
  // Now we need to catch the generic error
  res.json({
    error: err
  });
}