Why Does My Promise Resolve Prematurely in Node.js with Express and Promises?

Node.js Express and Promises: Addressing Unpredictable Behavior

Cause of Unwait Promise

In your code, the promise created for the findUser function executes immediately, but the function itself is asynchronous. Hence, the promise resolves prematurely before findUser can retrieve data.

Implementing Proper Promise Execution

Modify your findUser function to return a promise instead of attempting to return values synchronously. Here's an example:

me.findUser = function(params, res) {
    var username = params.username;

    return new Promise(function (resolve, reject) {

      pool.getConnection(function (err, connection) {
        if (err) {
          reject(err);
          return;
        }

        connection.query('select Id, Name, Password from Users ' +
            'where Users.Name = ?', [username], function (err, rows) {
            connection.release();
            if (err) {
                reject(err);
            } else {
                resolve(rows);
            }
        });
      });
    });
}

Error Handling

The "error handler second" message appears because the error handler in the second promise is rejected when findUser encounters an error. To fix this, modify the code as follows:

promise.then(function(data) {
            return new Promise(function (resolve, reject) {
                loginC.doSomething(data);

                if (success) {
                    console.log("Success 2");
                    resolve(data);
                } else {
                    console.log("Failed 2");
                    reject("Error in doSomething");
                }
            });
        }).catch(function (reason) {
            console.log("Error in findUser: " + reason);
        });

Additional Notes

• Make sure to handle database connection errors in the connection callback.
• Avoid relying on synchronous methods for asynchronous operations.
• Promises are used for chaining asynchronous operations and handling outcomes reliably.

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