JSON data if/else parse

Question

I am doing some long polling (ajax) and I am looping the following portion of code.. There is code being executed above and below. This code is part of an internal messaging system. A certain portion of the page wil blink when a message arrives. If the user checks the message, it will remove the dash_notify from the JSON response, which needs to turn off the blinking. See below:

if (data.dash_notify == '1') {
    var x = '#dash_notif_blink';

    function blinking(x) {
        timer = setInterval(blink, 10);

        function blink() {
            x.fadeOut(400, function () {
                x.fadeIn(400);
            });
        }
    }

    console.log("initiate_dash");
    blinking($(x));
} else if (!data.dash_notify) {
    console.log("good");

    clearInterval(timer);
}

The following JSON response that gets sent to this code is:

{"current_date_time":"January 8, 2013 - 4:02 pm","dash_notify":"1"}

It understand the initial blink IF the above data gets passed. If the following gets passed:

{"current_date_time":"January 8, 2013 - 4:02 pm"}

Then it throws an error:

Uncaught ReferenceError: timer is not defined 

I cannot figure out how to fix the "else" portion working properly. If the code is initiated when the full dash_notify:1 response is sent, it works perfect. The button will blink, then if the user checks the message, it will no longer send dash_notify:1 and the button stops blinking. But if the code is initiated when dash_notify:1 is NOT set, it doesn't know what to do with the ClearInterval.

Basically I need the else portion fixed.

I have tried using different typeOf === undefined snippets, but it doesn't work.

Any help is appreciated.

Thank you!

EDIT:

This is currently working.. Timer is now defined above the statement

if(data.dash_notify == '1'){

                            var x = '#dash_notif_blink';

                        console.log("initiate_dash");
                        blinking($(x));

                        }else if (typeof timer != "undefined" && timer) { 
                            clearInterval(timer);
    }               
                    }

This is working, but sometimes it trys to kill the timer but it doesn't actually do it. This happens every so often.

Answer 1

This is now working beautifully. *Thank you to everyone who helped!*

if(data.dash_notify === '1' && t === null ){

                    var x = '#dash_notif_blink';

                    function blinking(x) {
                        var timer = setInterval(blink, 10); //note the var keyword for best practice

                        function blink() {
                            x.fadeOut(400, function () {
                                x.fadeIn(400);
                            });
                        }
                        return timer;
                    }

                    console.log('initiate_dash_alert');

                    // Data is passed. Parse to see if dash alert should be called. Secondary protection for
                    // multiple timer creation.
                    if(t){return;}else{t = blinking($(x));}




                }else if (!data.dash_notify){    
                    clearInterval(t);
                    console.log('clear_dash_alert');
                    t = null;
                }else{
                    console.log(t);
                    console.log('no_push_events');

                }