Unhandled promise rejection: Cannot set headers after they are sent to the client

Issue

I don't know why this errors kept coming. I searched for all possible solutions on the internet still I didn't find any. Here is my node function for API call:

exports.GetEmployeeConfirmationList = function (req, res) {
    var request = dbConn.request();
    request.execute(storedProcedures.GetEmployeeConfirmationList).then(function (response) {
        res.status(200).send({
            success: true,
            data: response.recordset
        });
    }).catch(function (err) {
        res.status(200).send({
            success: false,
            message: err.message
        });
    });
};

How to overcome this problem?

Solution

Modify your code to use arrow function as res object is losing its scope. When GetEmployeeConfirmationList callback is called it doesn't know about res object hence undefined for it. So while executing res.status it throws an exception and comes in catch block, where it again executes res.status and it breaks again and leads to Unhandled promise rejection. You can capture the err object and log it in finally block to check if it is happening so.

exports.GetEmployeeConfirmationList = function (req, res) {
    var request = dbConn.request();
    request.execute(storedProcedures.GetEmployeeConfirmationList).then((response) => {
        res.status(200).send({
            success: true,
            data: response.recordset
        });
    }).catch((err) => {
        res.status(200).send({
            success: false,
            message: err.message
        });
    });
};

Answered By - Suresh Prajapati