购物清单的js代码有问题

Question

function addItem() {
  var li = document.createElement("li");
  var x = document.getElementByClassName("myInput").value;
  var t = document.createTextNode(x);

  li.appendChild(t);

  document.getElementByClassName("myOL").appendChild(li);
  document.getElementByClassName("myInput").value = "";
}