如何异步获取TextBox的AutoComplete数据？

<ul id="autoCompleteList"></ul>

function getAutoCompleteData() {
  var input = document.getElementById("myTextBox").value;
  var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function() {
    if (xhr.readyState == 4 && xhr.status == 200) {
      var data = JSON.parse(xhr.responseText);
      showAutoCompleteData(data);
    }
  };
  xhr.open("GET", "https://api.example.com/autocomplete?q=" + input, true);
  xhr.send();
}

function showAutoCompleteData(data) {
  var list = document.getElementById("autoCompleteList");
  list.innerHTML = "";
  for (var i = 0; i< data.length; i++) {
    var li = document.createElement("li");
    li.appendChild(document.createTextNode(data[i]));
    list.appendChild(li);
  }
}