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Res.redirect is not a function while using express in a nodejs webapp

I am trying to redirect to '/admin' route if the required data gets updated successfully but I am getting the error that res.redirect is not a function. I have tried writing return res.redirect also but it is also not working. Node experts, please help. Here I am just finding the student record on it's reg.no. basis and updating the record with its marks and redirecting to the admin page.
app.post('/admin/midterm/marks',(req,res)=>{
var m_written=[];
var m_practical=[];
var myjson=JSON.stringify(req.body);
course.subjects.map(sub=>{
if(!Array.isArray(req.body[`${sub}`]))
{
var p={subject:sub,mark:req.body[`${sub}`]}
m_written.push(p);
}
else{
var p={subject:sub,mark:req.body[`${sub}`][0]};
var q={subject:sub,mark:req.body[`${sub}`][1]};
m_written.push(p);
m_practical.push(q);
}
});
var first={
sem:course._id,
marks_sem:[{
term:ms,
m_written:m_written,
m_practical:m_practical
}]
}
if(!StudentRecord.total.length )
{
Student.updateOne({_id:check_Id},{total:first},function(err,res){
if(err)
{console.log("error");}
res.redirect('/admin');
});
}
else{
var flag=0;
StudentRecord.total.map(record=>{
if(record.sem==required_sem)
{
flag=1;
record.marks_sem.push(first.marks_sem);
Student.updateOne({_id:check_Id},{total:StudentRecord.total},function(err,res){
if(err)
{console.log("error");}
res.redirect('/admin');
});
}
});
if(flag==0)
{
StudentRecord.total.push(first);
Student.updateOne({_id:check_Id},{total:StudentRecord.total},function(err,res){
if(err)
{console.log("error");}
res.redirect('/admin');
});
}
}});

You override res in your callbacks. Name the second parameter in the callbacks result and everything will work fine.
app.post("/admin/midterm/marks", (req, res) => {
var m_written = [];
var m_practical = [];
var myjson = JSON.stringify(req.body);
course.subjects.map((sub) => {
if (!Array.isArray(req.body[`${sub}`])) {
var p = { subject: sub, mark: req.body[`${sub}`] };
m_written.push(p);
} else {
var p = { subject: sub, mark: req.body[`${sub}`][0] };
var q = { subject: sub, mark: req.body[`${sub}`][1] };
m_written.push(p);
m_practical.push(q);
}
});
var first = {
sem: course._id,
marks_sem: [
{
term: ms,
m_written: m_written,
m_practical: m_practical,
},
],
};
if (!StudentRecord.total.length) {
Student.updateOne({ _id: check_Id }, { total: first }, function (err, result) {
if (err) {
console.log("error");
}
res.redirect("/admin");
});
} else {
var flag = 0;
StudentRecord.total.map((record) => {
if (record.sem == required_sem) {
flag = 1;
record.marks_sem.push(first.marks_sem);
Student.updateOne(
{ _id: check_Id },
{ total: StudentRecord.total },
function (err, result) {
if (err) {
console.log("error");
}
res.redirect("/admin");
}
);
}
});
if (flag == 0) {
StudentRecord.total.push(first);
Student.updateOne(
{ _id: check_Id },
{ total: StudentRecord.total },
function (err, result) {
if (err) {
console.log("error");
}
res.redirect("/admin");
}
);
}
}
});

Mysql node.js async, wait for query to complete

Been trying everything to get this to work specifically the async each method. for (const element of resultsHistory) didn't work either.
I'm trying to modify the result array from a previous query by running a foreach over it and doing a mysql query.
However this needs to wait for the query to complete.
Is there a way to access these results without the setTimeout(function() { } I put manually in order to wait for the query to finish?
function getUserLikes(params, callback) {
var usersArrayCat = [];
console.log(`length of array ${params.length}`)
// 1 here means 1 request at a time
async.eachLimit(params, 1, function (element, cb) {
element.liked = 0;
var queryLiked = `SELECT * from users_likes WHERE user_id = \"${req.body.userid}\" AND product_id = \"${element.product_id}\"`;
connectionPromise.query(queryLiked, function (err, result) {
if (!result) {
} else if (result.length == 0) {
} else {
element.liked = result[0].userlike;
usersArrayCat.push(element);
// console.log(usersArrayCat);
cb();
}
})
}, function (err) {
if (err) return callback(err);
callback(null, usersArrayCat)
});
};
getUserLikes(resultsHistory, function (e) {
console.log(e);
});
if(!res.headersSent) {
setTimeout(function() {
res.send(JSON.stringify({"status": 200 ,"error": null, "top3":resultsHistory}));
}, 150);
}

Managed to get it working like this, but still not sure if this is the right way.
async function getUserLikes(resultsHistory) {
for (const element of resultsHistory) {
element.liked = 0;
let queryLiked = `SELECT * from users_likes WHERE user_id = \"${req.body.userid}\" AND product_id = \"${element.product_id}\"`;
let liked = await conn2.query(queryLiked);
if (liked[0]) {
element.liked = liked[0].userlike;
}
}
if(!res.headersSent) {
conn2.release();
let newres = resultsHistory.sort(
firstBy(function (v1, v2) { return v2.rating - v1.rating; })
.thenBy(function (v1, v2) { return v2.dranktimes - v1.dranktimes; })
).filter( function(history) {
return history.event === eventName;
}).slice(0, 3);
res.send({"status": 200 ,"error": null, "top3":newres});
}
}
getUserLikes(resultsHistory);

See my answer:
function getUserLikes(params, callback) {
var usersArrayCat = [];
console.log(`length of array ${params.length}`)
// 1 here means 1 request at a time
async.eachLimit(params, 1, function (element, cb) {
element.liked = 0;
var queryLiked = `SELECT * from users_likes WHERE user_id = \"${req.body.userid}\" AND product_id = \"${element.product_id}\"`;
connectionPromise.query(queryLiked, function (err, result) {
if (!result) {
} else if (result.length == 0) {
} else {
element.liked = result[0].userlike;
usersArrayCat.push(element);
// console.log(usersArrayCat);
}
cb();
})
}, function (err) {
if (err) return callback(err);
callback(null, usersArrayCat)
});
};
getUserLikes(resultsHistory, function (e, usersArrayCat) {
if (e) {
console.log(e);
return res.send({status: 400, error: e}); // your error response
}
console.log(usersArrayCat); // your usersArrayCat with liked property
res.send(JSON.stringify({ // why your need return a string intead of json object ???
"status": 200,
"error": null,
"top3": usersArrayCat // I think return `usersArrayCat` is a right way
}));
});

Run loop on the server with node.js

Let's say i need to constantly collecting some data from a lot of clients and in parallel running some complex loop that solving some stuff with this data. How can i do it? Should i just write this in my piece of code:
app.get('/', function(req, res) {
res.sendFile(__dirname + '/public/views/index0.html');
});
io.sockets.on('connection', function(socket) {
// SOME STUFF WITH THE SOCKET
socket.on('disconnect', function(data) {
//SOME OTHER STUFF
});
});
while(...) {
//THE LOOP STUFF
}
Or i need to use the setTimeout() and setInterval() functions? How can i do the loop on the server that runs in parallel with the callbacks' stuff?

Don’t use while for make it, this block a thread. setTimeout() will run only once. You need to use setInterval() function.

You can use the async module to handle the async operation with the callback or use promise to avoid callback.
Here how I handle a complex async for each operation, that might helpfull to you get idea handeling ayncs forach
var cond = { _schedule: schedule_id }; // find curse by schedule id
Course.find(cond, function (err, courses) {
if (err) {
callback({ "success": false, "message": "Not able to update" });
} else {
async.forEachLimit(courses, 1, function (course, coursesCallback) {
async.waterfall([
function (callback) {
var schedule_date = moment(change_data.date).format('YYYY-MM-DD') + "T00:00:00.000Z"
var Assignmentcond = {
assignment_schedule_order: {
$gte: schedule_date
},
_course: course._id,
_schedule: schedule_id,
_user: userid
};
Assignment.find(Assignmentcond)
.populate({
path: '_course',
})
.lean()
.sort({ assignment_schedule_order: 1 })
.exec(function (err, AssignmentList) {
if (err) {
callback(null, '');
} else {
//console.log("------------------AssignmentList---------------------------");
//console.log(AssignmentList);
async.forEachLimit(AssignmentList, 1, function (ThisAssignmentCell, ThisAssignmentCellCallback) {
async.waterfall([
function (callback) {
var SearchObj = items;
var lebelObject = {};
for (var i = 0, flag = 0, insert = 0; i < SearchObj.length; i++) {
if (SearchObj[i].date == ThisAssignmentCell.assignment_schedule_date) {
flag = 1;
}
if (flag == 1 && SearchObj[i].label != "") {
if (ThisAssignmentCell.day == SearchObj[i].day_index) {
insert = 1;
var lebelObject = SearchObj[i];
break;
}
}
}
callback(null, ThisAssignmentCell, lebelObject, insert);
},
function (ThisAssignmentCell, SearchObj, insert, callback) {
console.log('----------------------');
console.log('ThisAssignmentCell', ThisAssignmentCell);
console.log('SearchObj', SearchObj);
console.log('----------------------');
if (insert > 0) {
var query = { _id: ThisAssignmentCell._id },
fields = {
assignment_date: moment(SearchObj.date).format('MM/DD/YYYY'),
assignment_schedule_date: moment(SearchObj.date).format('YYYY-MM-DD'),
assignment_schedule_order: new Date(SearchObj.date),
day: SearchObj.day_index,
dayNum: SearchObj.weekday_num
},
options = { upsert: false };
Assignment.update(query, fields, options, function (err, affected) {
callback(null, '');
});
} else {
// var cond = { _id: ThisAssignmentCell._id};
// Assignment.remove(cond)
// .exec(function (err, cnt) {
// callback(null, '');
// });
}
}
], function (err, result) {
// result now equals 'done'
console.log('done')
ThisAssignmentCellCallback();
});
}, function (err) {
console.log("Assignment For Loop Completed");
callback(null, AssignmentList);
});
}
});
}
], function (err, result) {
// result now equals 'done'
console.log('done')
coursesCallback();
});
}, function (err) {
console.log("courses For Loop Completed");
});
}
});

Sending array data from server to client in Meteor

So I'm trying to send my data from my server code to my client code, yet it's returning undefined. Not sure what to do as I've been stuck here for a while.
I used these packages:
https://github.com/meteorhacks/npm
https://www.npmjs.com/package/wiki-infobox
Rappers = new Mongo.Collection(null)
var page = 'Tupac'
var language = 'en'
var rappers = null
var texts
var rappers2
if (Meteor.isClient) {
getGists = function getGists(user, callback) {
Meteor.call('getGists', user, callback);
}
Meteor.startup(function() {
rappers2 = []
function call(text, callback) {
Meteor.call('getWikiStuff', rappers2, function(err, result) {
console.log(result)
})
var timer = setTimeout(function() {
callback()
}, 4000)
}
function consoleit() {
console.log(rappers2)
}
call('hello', consoleit)
})
}
if (Meteor.isServer) {
Meteor.startup(function() {
Meteor.methods({
getWikiStuff: function(rappers3) {
var infobox = Meteor.npmRequire('wiki-infobox')
var bound = Meteor.bindEnvironment(function(callback) {
callback()
});
console.log("HERE")
bound(function() {
infobox(page, language, function(err, data) {
if (err) {
return
}
rappers = data.associated_acts
for (var x = 0; x < rappers.length; x++)
if (rappers[x].text != undefined) {
var yo = rappers[x].text
rappers3.push(yo)
}
for (var value of rappers3)
console.log(value)
})
})
return rappers3
}
})
})
}

Push data to out side async function

I still do not handle well the asynchronous functions, I have an array of items, and I'm trying to for each item calculate some values and push to another array outside of the async function. Then I want to make some statistics calculation and send to front end. It's server side, nodejs handler, my code:
exports.register = function (plugin, options, next) {
function isInArray(value, array) {
return array.indexOf(value) > -1;
}
function statistics(values) {
var sum = math.sum(values);
var max = math.max(values);
var min = math.min(values);
var stddev = math.std(values);
var mean = math.mean(values);
var count = values.length;
}
plugin.route({
method: 'GET',
path: '/statistics/{orgId}/layout/{layoutId}',
config: {
pre: [
authorize(hasRole(['OPERATIONAL', 'STRATEGIC', 'LOP', 'TACTICAL']))
],
handler: function (request, reply) {
Category.find()
.where('organization')
.equals(request.params.orgId)
.exec(function (err, categories) {
var weight = [];
var price = [];
var volume = [];
var thisAR = [];
if (err || categories === null) {
return reply(Boom.badRequest('Categoria inexistente'));
} else {
Location.findById(request.params.layoutId)
.exec(function (err, layout) {
if(err) {
console.log(err);
}
var searchItems = function searchItems(category, next) {
Item.find()
.where('category')
.equals(category._id)
.exec(function (err, items) {
if (err) {
console.log(err);
} else {
var valuesToCalculate = [];
var itemsFiltered = [];
_.forEach(items, function(item) {
if(item.location && item.location !== null) {
if(isInArray(item.location.toString(), layout.contents)) {
itemsFiltered.push(item);
}
}
});
valuesToCalculate.push(itemsFiltered.length * category.data.weight);
valuesToCalculate.push(itemsFiltered.length * category.data.price);
valuesToCalculate.push(itemsFiltered.length * category.data.volume);
next(valuesToCalculate);
}
});
}
var onFinish = function onFinish(value, err) {
if(err) {
console.log(err);
}
console.log(value);
thisAR.push.apply(value);
}
async.each(categories, searchItems, onFinish);
console.log(thisAR);
//var arrays = [statistics(weight), statistics(price), statistics(volume)];
//return arrays;
});
}
});
}
}
});
next();
};

A few things stand out to me about this. First, you only call reply if there is an err or categories is null. Also, you are attempting to pass a non null value to an async.each callback. According to this: https://github.com/caolan/async#eacharr-iterator-callback, "if no error has occurred, the callback should be run without arguments or with an explicit null argument". I think you may misunderstand how the onFinish callback works with async.each.. it is not called for each item, it is called when all of the iterator functions have completed. So, rather than pushing items onto thisAR in onFinish, you should do so inside searchItems. I think this should work:
exports.register = function (plugin, options, next) {
function isInArray(value, array) {
return array.indexOf(value) > -1;
}
function statistics(values) {
var sum = math.sum(values);
var max = math.max(values);
var min = math.min(values);
var stddev = math.std(values);
var mean = math.mean(values);
var count = values.length;
}
plugin.route({
method: 'GET',
path: '/statistics/{orgId}/layout/{layoutId}',
config: {
pre: [
authorize(hasRole(['OPERATIONAL', 'STRATEGIC', 'LOP', 'TACTICAL']))
],
handler: function (request, reply) {
Category.find()
.where('organization')
.equals(request.params.orgId)
.exec(function (err, categories) {
var weight = [];
var price = [];
var volume = [];
var thisAR = [];
if (err || categories === null) {
return reply(Boom.badRequest('Categoria inexistente'));
} else {
Location.findById(request.params.layoutId)
.exec(function (err, layout) {
if(err) {
console.log(err);
}
var searchItems = function searchItems(category, next) {
Item.find()
.where('category')
.equals(category._id)
.exec(function (err, items) {
if (err) {
console.log(err);
} else {
var valuesToCalculate = [];
var itemsFiltered = [];
_.forEach(items, function(item) {
if(item.location && item.location !== null) {
if(isInArray(item.location.toString(), layout.contents)) {
itemsFiltered.push(item);
}
}
});
valuesToCalculate.push(itemsFiltered.length * category.data.weight);
valuesToCalculate.push(itemsFiltered.length * category.data.price);
valuesToCalculate.push(itemsFiltered.length * category.data.volume);
thisAR.push.apply(valuesToCalculate);
}
next(err);
});
}
var onFinish = function onFinish(err) {
if(err) {
console.log(err);
}
console.log(thisAR);
// call reply here
}
async.each(categories, searchItems, onFinish);
console.log(thisAR);
//var arrays = [statistics(weight), statistics(price), statistics(volume)];
//return arrays;
});
}
});
}
}
});
next();
};

I can't comment since I'm new but it seems that just removing the .apply in thisAR.push.apply(valuesToCalculate); will return a full array to your console.log.