var startTime = new Date().getTime();

var time   = 0;

var collided  = false;

var engine;

​

function collision(){

  collided = true;

  time = parseInt((new Date().getTime()-startTime)/1000, 10);

}

​

function game(){  

  if(collided){

    alert("GAME OVER "+ time); 

    return clearInterval( engine ); 

  }

  /* GAME LOGIC HERE */

}

​

engine = setInterval(function(){ 

   game();

},25);

​

$('button').click(collision);