res is not defined in Node.js (Mongoose) - node.js

Question

How can I put res in a normal function i.e not an exported one which is not part of routes?
function createNewStudent(v,callBackOne){
if (callBackOne) {
studentInfo.callBackOneStudent = callBackOne;
}
// common filter json
var filterjson = common.defaultFilterJson();
filterjson['active'] = true;
filterjson['email'] = v.email;
// student initialization
var student = new Student(v);
async.waterfall([
function (done) {
student.save(function (err) {
if (!err) {
studentInfo.callBackOneStudent();
Employee.update({_id: student.created_by},{"$push": { "students": student._id } }).exec(function (err, employee) { });
done();
}
});
}
}
});
},
function (done) {
var url = config.mailer.studentActivateUrl + student._id;
---error is here-----
res.render('modules/users/server/templates/student-confirmation-email', {
name: student.first_name + ' ' + student.last_name,
appName: 'GAIPP',
url: url
}, function (err, emailHTML) {
done(err, emailHTML, student);
});
}
});
My error is 'res' is not defined. Can anyone please help me to solve this error?

Answer 1

The only way that you can put res in a function is if you somehow supply it to that function at runtime. Remember that res is meaningful only in request handling. Outside of the request handler your function couldn't even know which request to respond to because there might be several requests served at the same time.
If you want to have a function that has access to res then you have those options:
Use a nested function in your request handler, e.g.
app.get('/foo', function (req, res) {
function x() {
// you can use res here
}
x();
});
Add res as an argument:
function x(res) {
// you can use res here
}
app.get('/foo', function (req, res) {
x(res);
});
Another option would be to add a callback to your function that would be passed by the handler:
function x(args, cb) {
// you cannot use res here
// but you can call the callback:
cb(null, 'something');
}
app.get('/foo', function (req, res) {
x(function (err, data) {
if (err) {
// handle error
}
// use res here with data supplied by x()
res(data);
});
});
Instead of using callback your x() function could also return a promise.