javascript - Timer Start button -

hi i'm making game involves count down timer. want game start when timer button clicked @ moment timer begins on own. have looked @ few different questions answered haven't worked me. suggestions?

     var seconds = 60;      function secondpassed() {         var minutes = math.round((seconds - 30)/60);         var remainingseconds = seconds % 60;         if (remainingseconds < 10) {            remainingseconds = "0" + remainingseconds;           }         document.getelementbyid('countdown').innerhtml = minutes + ":" + remainingseconds;         if (seconds == 0) {           clearinterval(countdowntimer);           document.getelementbyid('countdown').innerhtml = "times up!!!";         } else {            seconds--;         }      }       var countdowntimer = setinterval('secondpassed()', 1000); 

add setinterval button's click listener:

var btn = document.getelementbyid('button_id'); btn.addeventlistener('click', function() {     setinterval('secondpassed()', 1000); }); 

jsfiddle demo