Why doesn't promise.catch() catch the error?

Question

JavaScript

Code without error (works fine):

let userInsert = new Promise((resolve, reject) => {
            db.query('INSERT INTO users (email, password) VALUES (?, ?)', [user.email, user.password])
        });

        userInsert
            .catch(function (err) {
                console.log('error');
            });

Code with a request error (crashes the program, although it should be caught in catch):

let userInsert = new Promise((resolve, reject) => {
            db.query('INSERT INTO users (email, passwordError) VALUES (?, ?)', [user.email, user.password])
        });

        userInsert
            .catch(function (err) {
                console.log('error');
            });

Check if the promise is catching errors. Works fine.

let p = new Promise((resolve, reject) => {
      // то же что reject(new Error("o_O"))
      throw new Error("o_O");
    })
    
    p.catch(alert('error'));

Actually, why doesn't the second code catch the error? And outputs to the console:

Error: ER_BAD_FIELD_ERROR: Unknown column 'passwordError' in 'field list'

Answer 1

You don't resolve or reject anything, so this promise will never go further down the chain.
It is obvious that db.query is asynchronous, but since it did not receive a callback, it throws its exception into the general thread, by this moment the promise handler function has already been successfully completed, naturally it does not catch an error.
Much of course depends on the database driver, but I suspect that you need to do this:

let userInsert = new Promise((resolve, reject) => {
  db.query('INSERT INTO users (email, password) VALUES (?, ?)', [user.email, user.password], err => {
    if(err) {
      reject(err);
      return;
    }
    resolve();
  });
});

Answer 2

Well, maybe he catches an error inside himself and displays it in the console. and the promise rejects, for example

Answer 3

Promise.catch is not part of the try/catch statement. promise.catch is just a shortcut for everything that comes promise.then(null, function() {})with it.

Answer 4

It is advisable to specify which driver for which database you are using. It is strange for me to see a blocking database request in the node.js code when non-blocking calls with callbacks are used for almost any i / o operations. It is possible that you need to manually throw an exception in the callback/reject the promise if err is present, in the callback call after the request

Answer 5

It can only catch synchronous exceptions.
Simple example:

let p = new Promise((resolve, reject) => {
    setTimeout(() => {
        throw 'WTF';
    }, 0);
});

p.catch( console.log );

Well, in general, it is very strange to see the creation of a promise in which neither resolve nor reject are called.
Correctly it should be something like this:

let userInsert = new Promise((resolve, reject) => {
  db.query(
    'INSERT INTO users (email, password) VALUES (?, ?)',
    [user.email, user.password],
    (err, result) => {
      if (err) {
        reject(err);
      } else {
        resolve(result);
      }
    }
  )
});