获取textarea框的滚动条有问题

textarea::-webkit-scrollbar {
  width: 12px;
}

textarea::-webkit-scrollbar-track {
  background: #f1f1f1;
}

textarea::-webkit-scrollbar-thumb {
  background: #888;
}

textarea::-webkit-scrollbar-thumb:hover {
  background: #555;
}

var textarea = document.getElementById("myTextarea");
var scrollTop = textarea.scrollTop;
var scrollLeft = textarea.scrollLeft;

var textarea = document.getElementById("myTextarea");
textarea.scrollTop = 100;
textarea.scrollLeft = 50;