running multiple instances of ajax function - only second instance updates

Question

I am having difficulty calling multiple instances of the same Ajax.Request function. (I'm using the Prototype framework). Here is the function:

function send_SMS(id)
{
    status_id = 'status_link_' + id;

    new Ajax.Request('sendSMS.php', 
    {
        method:'post',
        parameters: {link_id: id},
        onCreate: function(){
            $(status_id).update("sending...");
        }, 
        onSuccess: function(transport){
            if (transport.responseJSON.success) {
                $(status_id).update("sent");
            } else {
                $(status_id).update("unable to send");
            }
        },
        onFailure: function(){ 
            $(status_id).update("unable to send");
        }       
    });
}

If I call this function twice with 2 different id numbers i.e.:

send_SMS("1");
send_SMS("2");

only the second ID is updated by the onSuccess function. The sendSMS.php file is successfully run twice (as the name suggests it sends an SMS message and indeed the 2 messages are successfully sent), but the onSuccess function seems to only be called the second time.

Is the javascript confusing the 2 instances?

Answer 1

I think this is because status_id is a global variable, and therefore enters in the context of your both calls within the callback where its reference is being called:

onSuccess: function(transport){
        if (transport.responseJSON.success) {
            $(status_id).update("sent");
        } else {
            $(status_id).update("unable to send");
        }
    }

The thing is, the onSuccess callback will compile when it is called, with its context at that moment. And at that moment, the status_id will be equal to "status_link_2", because most chance that your call to send_SMS("2"); will come before the return of the first sms_send call.

A solution would be to:

• send the id within the ajax call, and retrieve it in the response to build your status_id variable, or
• use synchrone mode so the sms1 return comes back before the call of sms2.