Javascript function returns undefined error

Question

In my Cordova android app i am using getDeviceId function to get the unique device id.

function getDeviceId(){
        var temp;   
        newid=cordova.require('org.apache.cordova.uuid.UniqueDeviceID');
            newid.getDeviceID(success,fail);
            function  success(uuid){
              //this works 
              alert("inside function"+uuid);
              temp=uuid;
            }
            function fail(err){
             // alert("error"+err);
             }
           return temp;
        }

And i am calling this function like this way

var deviceId=getDeviceId();
//undefined error
alert("from function"+deviceId);

I will get device-id successfully inside the function,but the return value will give undefined error.

Answer 1

Use promise!

Short answer:

function getDeviceId(success, fail){
    return cordova.require('org.apache.cordova.uuid.UniqueDeviceID').getDeviceID(success, fail);
}

Better answer:

function getDeviceId(){
    var temp; //assume this as cache, this must be outside of this function scope, but for the sake of example
    var defer = q.defer(); //or any other promise libraries
    if(!temp){
        var cordova = cordova.require('org.apache.cordova.uuid.UniqueDeviceID');
        cordova.getDeviceID(function(uuid){
            temp = uuid;
            defer.resolve(uuid); //or other api depend on library
         }, function(err){
            temp = null; //clear cache on errors
            defer.reject('Could not get device id');
         });
    } else {
        defer.resolve(temp);
    }
    return defer.promise; //or other api depend on library   
}

Specific answer to you:

function getDeviceId(success, fail){
    return cordova.require('org.apache.cordova.uuid.UniqueDeviceID').getDeviceID(success, fail);
}

and then

getDeviceId(function(uuid){
    console.log(uuid); //this might be object, so drill to specific field
    alert("from function" + uuid);
}, function(errorMessage){
    alert(errorMessage);
});

Advice:

Checkout greate article about promises in details