I need someone to tell me how to cancel or clear the timer on this function.

```
//Html
    <a id="button" data-url="http://url.com">Click me!</a>

    Redirecting in <span id="timer"></span> seconds...
    <a href="javascript:void(0)" class="cancel">Cancel</a>
// jS
    $('a#button').click(function() {
        var url = $(this).attr("data-url");
        if( url.indexOf("http://")!==0 ){
                url = "http://"+url;
            }
        var seconds = 5,
            el = $('#timer')
        el.text(seconds)
        setTimeout(function countdown() {
            seconds--
            el.text(seconds)
            if (seconds > 0) {
                setTimeout(countdown, 1000)
            }
            else {
                window.open( url , "_self" )
            }
        }, 1000)
    })

    $('a.cancel').click(function(){
        clearTimeout(countdown);
    });

```

Also tell me what I"m doing wrong and why this isn't working.