server:

app.post("/login", (req, res) => {
    var gmail = req.headers.gmail;
    var username = req.headers.username;
    var password = req.headers.password;

    console.log(gmail, password, username);
    var sql = "SELECT gmail FROM Accounts WHERE gmail = ?";
    sql = mysql.format(sql, gmail);

    var sql1 = "SELECT username FROM Accounts WHERE username = ?";
    sql1 = mysql.format(sql1, username);
    var checks = [];



    (async () => { 
 
        console.log("test");
        con.query(sql, function(err, result){
            console.log(result);
            if (err) console.log("error");
            if (result.length == 1)
            {
                checks[0] = true;
                console.log(checks[0]);
            }
        })
 

        con.query(sql1, function(err, result){
            console.log(result);
            if (err) console.log("error");
            if (result.length == 1)
            {
                checks[1] = true;
                console.log(checks[1]);
            }
        })
 

        con.query("SELECT password FROM Accounts", async function(err, result){
            console.log(result);
            if (err) console.log("error");
            const Hashes = result;
            for(let i = 0; i < Hashes.length; i++){
                await bcrypt.compare(password, Hashes[i].password, (err, result) => {
                    if (result)
                    {
                        checks[2] = true;
                        console.log(checks[2]);
                        if (checks[0] == true && checks[1] == true) {
                
                            res.json("all good");
                            console.log("test1");
                        }
                    }
                })
                
                
            } 
            
        })

      
        
        



    })();
  });

i tried to login in but i get this error: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
at ServerResponse.setHeader (_http_outgoing.js:558:11)
at ServerResponse.header (/Users/ahmedm.fawzy/dev_nanos/learning/react/projects/exam/exam-app/server/node_modules/express/lib/response.js:795:10)
at ServerResponse.send (/Users/ahmedm.fawzy/dev_nanos/learning/react/projects/exam/exam-app/server/node_modules/express/lib/response.js:175:12)
at ServerResponse.json (/Users/ahmedm.fawzy/dev_nanos/learning/react/projects/exam/exam-app/server/node_modules/express/lib/response.js:279:15)
at /Users/ahmedm.fawzy/dev_nanos/learning/react/projects/exam/exam-app/server/server.js:151:33 {
code: ‘ERR_HTTP_HEADERS_SENT’
}
[nodemon] app crashed – waiting for file changes before starting…
at the server side