var numbers = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8];
var buttons = document.querySelectorAll("button");
var lastKnownButtonId = undefined;
var lastKnownButtonNumber = undefined;
var wait = false;

shuffle(numbers);
distributeNumbers();


function distributeNumbers() {
  for (i = 0; i < buttons.length; i++) {
    buttons[i].dataset.number = numbers[i];
  }
}

function shuffle(array) {
  var j, x, i;
  for (i = array.length - 1; i > 0; i--) {
    j = Math.floor(Math.random() * (i + 1));
    x = array[i];
    array[i] = array[j];
    array[j] = x;
  }
  return array;
}