async function shuffle(data, label) {
  let counter = data.length;
  let temp = 0;
  let index = 0;
  while (counter > 0) {
    index = (Math.random() * counter) | 0;
    counter--;
    // data:
    temp = data[counter];
    data[counter] = data[index];
    data[index] = temp;
    // label:
    temp = label[counter];
    label[counter] = label[index];
    label[index] = temp;
  }
}
Shuffles data and label using Fisher-Yates algorithm.