CODEWITHSUNDEEP
javascriptnode.jsajax
Parndhaman M
Parndhaman M

Reputation: 31

Callback isn't called as many times as expected

Employee webpage makes Ajax calls to the node.js web server in a loop. Code as given. All data values are correct. I expect the callback UpdateTeamArr to be called n times where n is equal to the loop max - document.getElementById("deptSelect").options.length. But its called only once. Thanks for your effort and support.

Client side code:

for (var i = 1; i < document.getElementById("deptSelect").options.length; i++) {
    var objJSON = {
        "deptid": document.getElementById("deptSelect").options[i].dataset.id,
        "empid": selectedEmployeeId
    }   
    var strJSON = JSON.stringify(objJSON);
    var xmlhttp = new XMLHttpRequest(); 

    xmlhttp.open("post", "../../GetEmployeesTeams", true);
    xmlhttp.onreadystatechange = function() {
        if(xmlhttp.readyState === XMLHttpRequest.DONE && xmlhttp.status === 200) {
            UpdateTeamArr(xmlhttp);
        }
    }
    xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded;charset=UTF-8");
    xmlhttp.send("strJSON=" + strJSON);     
    }
}
function UpdateTeamArr(xmlhttp) {
}

Server code:

app.post('/GetEmployeesTeams', function(req, res) {
var connection = mysql.createConnection({
    host     : "127.0.0.1",
    port     : 3306,
    user     : "root",
    password : "root",
    database : "lighting"
});
var strJSON = req.param('strJSON');
var objJSON = JSON.parse(strJSON);

connection.connect();
connection.query("SELECT db_teamemp.teamid, db_department.id AS deptid FROM lighting.db_teamemp, lighting.db_department, lighting.db_team WHERE db_teamemp.empid='" + 
                    objJSON.empid + "' AND db_department.id='" + objJSON.deptid + "' AND db_teamemp.teamid=db_team.id AND db_team.dept=db_department.id;", 
                    function(err, result, fields) {
    if (err)
        throw err;
    else {
        connection.end();
        res.status(200);
        return res.send(result);
    }
    });
});

Upvotes: 1

Views: 78

Answers (2)

Elliot Nelson
Elliot Nelson

Reputation: 11557

Ah, you are using a var here for xmlhttp. A var is not block scoped, it's hoisted - that means this single var is used by all calls to UpdateTeamArr. I believe you are calling the function N times, but with the last response every time.

An easy test of this theory is simply changing var to let on that line.

Upvotes: 1

PabloQ
PabloQ

Reputation: 361

Why don't you try to perform just a single request to the server by creating a uniq JSONArray with a list containing all Employees id's inside your 'deptSelect'?

This way you send a response with also a list containing the other attributes for the employees in another JSONArray format, that you can iterate in the UpdateTeamArr function

Upvotes: 1

Related Questions