Node.Js return value from module within an asynchronous function

Question

Node.Js return value from module within an asynchronous function

I'm sening an id to a module checking if the message hjas been sent or not. After it has not been sent I 'm sending the message:

 var l = require('./control.js')
 sonuc = l.check(id);

And my module is

 exports.check = function(id, callback){
        try{
          client.query("SELECT req FROM messages where req = 0 and id = "+id,
          function (err, results, fields) {
            if (results.length > 0){
                callback(false);
                }else{
                callback(true);
                }
         });
         callback();
  }catch(err){
    console.log(err);
  }  
  }

But it's failing and returning undefined variable.

function
node.js
asynchronous

Answer 1

returning from an asynchronous function doesn't mean anything; the whole point of using a callback is so you can get the value at a later date:

var l = require('./control.js')
l.check(id, function(sonuc) {
  // Here the value of sonuc is set.
});

You may be interested in this screencast, which goes over the topic in a bit more detail.