如何在Javascript中从下拉列表中选择对象的键

var cities = {
  "New York": "美国",
  "London": "英国",
  "Paris": "法国",
  "Tokyo": "日本"
};

<select id="citySelect"></select>

var selectElement = document.getElementById("citySelect");

// 遍历对象字典的方法
for (var city in cities) {
  var optionElement = document.createElement("option");
  optionElement.value = city;
  optionElement.text = city;
  selectElement.appendChild(optionElement);
}

// 遍历数组的方法
var citiesArray = Object.keys(cities);
for (var i = 0; i < citiesArray.length; i++) {
  var optionElement = document.createElement("option");
  optionElement.value = citiesArray[i];
  optionElement.text = citiesArray[i];
  selectElement.appendChild(optionElement);
}

selectElement.addEventListener("change", function() {
  var selectedKey = selectElement.value;
  console.log("选中的键是：" + selectedKey);
});