How to counter incoming trade offer?

[Vanilla]

Hello, how did I counter an incoming trade offer?
I know that I need to use "offer.counter()", but I don't know how to use it.

 

I got this following code to counter an offer, but it will show an error "Cannot add item to an already-sent offer".

manager.on('newOffer', function(offer) {
   if (offer.partner.getSteamID64() == admin){

      //Counter an offer by adding new item
      offer.counter();
      offer.addMyItem({"appid": 753, "contextid": 6, "assetid": "5222324266"}); //error here
      offer.send(function(err, status){
         if (err){
            console.log("Error: "+err);
         }
         console.log("Status: "+status)
      });
   }
}

Can anyone show the correct code please? I would really appreciate it.

Thanks

Edited July 22, 2017 by Vanilla

[Dr. McKay]

offer.counter() returns a new TradeOffer object. You need to perform your changes on that TradeOffer that it returns.

[Vanilla]

offer.counter() returns a new TradeOffer object. You need to perform your changes on that TradeOffer that it returns.

So, I need to use offer.counter() to get tradeoffer object, make change on that, and send new trade offer?

Edited July 23, 2017 by Vanilla

[Dr. McKay]

Correct.

[Vanilla]

Correct.

 

Thanks, just successfully make a counter offer.

I only need to add "counter()" everytime I want to counter an offer.

 

This is the working counter offer code (for those who got same problem)

 

manager.on('newOffer', function(offer) {
   if (offer.partner.getSteamID64() == admin){

      //Counter an offer
      offer.counter().addMyItem({"appid": 753, "contextid": 6, "assetid": "5222324266"}); 
      offer.counter().send(function(err, status){
         if (err){
            console.log("Error: "+err);
         }
         console.log("Status: "+status)
      });
      //confirmation
   }
}

Edited July 23, 2017 by Vanilla

[Dr. McKay]

No, that's wrong. Don't call counter() more than once. Call it once and store the result in a variable.

[Vanilla]

No, that's wrong. Don't call counter() more than once. Call it once and store the result in a variable.

 

Lol, so that's why I'm unable to add new item. 

 

Now works like a charm, thanks.

 

manager.on('newOffer', function(offer) {
   if (offer.partner.getSteamID64() == admin){

      //Counter an offer by adding new item
      var counteroffer = offer.counter();
      counteroffer.addMyItem({"appid": 753, "contextid": 6, "assetid": "5222324266"}); 
      counteroffer.send(function(err, status){
         if (err){
            console.log("Error: "+err);
         }
         console.log("Status: "+status)
      });
      //confirmation
   }
}