Check if element has class [duplicate]

Answer 1

I suggest to check each container (not an array as in previous answer):

function checkawinner(box) {
  box.addEventListener("click", function(){
   if (box.classList.contains('winning')) {
        console.log('you win');
    } else {
        console.log('you lose');
   }
  }, false);
}

for (index = 0; index < boxes.length; ++index) {
  checkawinner(boxes[index]);  
}

A pen with "alerts": http://codepen.io/VsevolodTS/pen/BKBjpP