how to access function variable in anonymous function

Question

I have a function as

 var emailExists = function (email) {
   mongoose.model('User', UserSchema).
    count({
        email: email
    }, function (err, count) {
        if (err) console.log(err);
        return count;// how can i return this count
    });
 };

in another function i call emailExists

 var total = emailExists(email)
 console.log(total); // this gives undefined now

How can i get the return value from the anonymous function

EDIT: After adding callbacks from suggestions below

var emailNotExists = function (email, _callback) {
 mongoose.model('User', UserSchema).
    count({
        email: email
    }, function (err, count) {
        if (err)
            return _callback(err, null);
        return _callback(null, ((count == 0) ? true : false));
    });
};

Function where it is called

   UserSchema.path('email').validate(function (email) {
   // I need to return true or false value from this function
   // on true the validation will success
   // on false "Email is registered" message will get fired
   emailNotExists(email, function (err, total) {

       // I can retrieve the True/false value here           
       console.log(total);
   });
  }, 'Email is registered');

Is `mogoose.model` an asynchronous function? If so, anything that depends on the result of the callback function has to be done _in_ the callback. — Barmar, Feb 01 '14 at 13:02
@Barmar please see my edited question. I hope I am clear this time. — Sami, Feb 01 '14 at 13:29
Your first `return _callback(count)` is missing an argument to the callback. — Barmar, Feb 01 '14 at 13:33
@Barmar edited. I just want to return true/false from the emailNotExists() call in UserSchema.path.validate function. How can I do that — Sami, Feb 01 '14 at 13:47
If you know what "asynchronous" means, it should be obvious why that can't work. — Barmar, Feb 01 '14 at 13:52

score 3 · Accepted Answer · answered Feb 01 '14 at 13:02

3

Pass in a callback function:

var emailExists = function (email, _callback) {
   mongoose.model('User', UserSchema).
    count({
        email: email
    }, _callback);
 };

Then access the variable as follows:

emailExists(email, function(err, total) {
    console.log(total);
});

answered Feb 01 '14 at 13:02

Matt Way

32,319
10
79
85

In my opinion, too much overhead for what he wants to do – leblma Feb 01 '14 at 13:03
2

But it's the correct approach. If the callback is asynchronous, you can't access the result immediately. – Barmar Feb 01 '14 at 13:03
3

@leblma - not too much overhead imo, and better than creating a global variable as you have suggested ( imo ). Here everything is contained. – Rob Sedgwick Feb 01 '14 at 13:04
@leblma - Too much overhead? What does that even mean? – Matt Way Feb 01 '14 at 13:08
@MWay There's a much simpler way to do this, global variable. The code is more clean this way. – leblma Feb 01 '14 at 13:11
@leblma - No that idea is far from clean. Do you know if the `count()` function is or will ever be asynchronous? Callback functions keep it clean by containing everything. – Matt Way Feb 01 '14 at 13:14
@Mway Yes I know it cauz I'm god. – leblma Feb 01 '14 at 13:15
@MWay Doing callback is the right way. please see the edited question. – Sami Feb 01 '14 at 13:27
@MWay Accepting since your answer led me to right direction and answered my original question – Sami Feb 01 '14 at 14:56

score 0 · Answer 2 · answered Feb 01 '14 at 13:02

0

Use this code:

var total;
var emailExists = function (email) {
   mongoose.model('User', UserSchema).
    count({
        email: email
    }, function (err, count) {
        if (err) console.log(err);
        total = count;
    });
 };

Then you can access it: console.log(total);

answered Feb 01 '14 at 13:02

leblma

174
7

@Sami That's probably cause you forgot to mention that count is asynchronous. – flup Feb 01 '14 at 13:54
@leblma sorry for not mentioning the async functions. – Sami Feb 01 '14 at 13:57

score 0 · Answer 3 · answered Feb 01 '14 at 13:04

0

Try this.

var emailExists = function (email) {
 var result;
   mongoose.model('User', UserSchema).
    count({
        email: email
    }, function (err, count) {
        if (err) console.log(err);
        result =count;// how can i return this count
    });
  return result;
 };

answered Feb 01 '14 at 13:04

kjana83

398
3
16

1

This won't work if `mongoose.model` runs asynchronously, as I suspect it does. – Barmar Feb 01 '14 at 13:05
@kjana83 this doesn't work cause the function is asynchronous – Sami Feb 01 '14 at 13:28

how to access function variable in anonymous function

3 Answers3