How to disable warning/error log that resulted from react fetch?

Question

Greeting all. I am creating a simple single page application using reactjs for front-end and ReST API using nodejs for back-end development. However, when they are merged using fetch() from reactjs for login purpose, the console show a warning whenever login fail but none for succeed case.

React code:

fetch("/*api-url*//users/signin", {
        method: "POST",
        body: JSON.stringify(data),
        headers: {
          "Content-Type": "application/json"
        },
        credentials: "same-origin"
      })
      .then((response) => response.json())
      .then((result) => {
        if(result.error) return Promise.reject(result.error);

        this.setState({ isLoading: false });
        alert("Sign in successfully.");
        console.log("Login approved!");
        return null;
      })
      .catch((error) => {
        alert("Unable to sign in. Error: " + error);
      });

Nodejs code:

exports.signin = (req, res, next) => {
  const email = req.body.email;

  return checkEmail(email)
    .then(() => {
      return userDatabase.findByElement({email: email});
    })
    .then((snapshot) => {
      if(!snapshot.val()) return Promise.reject(ERROR.UNAUTHENTICATED);
      else {
        const userId = Object.keys(snapshot.val())[0];
        const user = Object.values(snapshot.val())[0];

        bcrypt.compare(req.body.password, user.password, (error, result) => {
          if(result) {
            const token = jwt.sign({
                email: user.email,
                userId: userId
              },
              env.jwt_key,
              {
                expiresIn: "1h"
              });

            return res.status(200).json({
              message: "Authetication success",
              token: token
            });
          }
          return httpResponse.respondError(res, ERROR.UNAUTHENTICATED);
        })

        return null;
      }
    })
    .catch((error) => {
      httpResponse.respondError(res, error);
    })
}

respondError = (res, error) => { 
  switch(error) {
    case ERROR.INVALID_ID:
      res.status(404).json({
        message: 'No valid entry found for provided ID',
        error: error
      });
      break;
    case ERROR.NO_DATA:
      res.status(404).json({
        message: 'No entries found',
        error: error
      });
      break;
    case ERROR.UNAUTHENTICATED:
      res.status(401).json({
        message: 'Authentication failed',
        error: error
      });
      break;
    default:
      res.status(500).json({ 
        error: error
      });
  }
}

I expect there will be no warning/error log like login success case, but there is a warning/error log if login failed as shown:

Output in console:
POST /*api-url*//users/signin 401       signin:1 (for case login failed)
Login approved!                        App.js:17 (for case login succeed)

May I know how to disable the warning/error log for the login failed case? Thanks in advance.