如何在页面加载时强制下拉列表选择？

window.onload = function() {
  var selectElement = document.getElementById("select-element-id");
  var event = new Event("change");
  selectElement.dispatchEvent(event);
}

select option:first-child {
  display: none;
}

window.onload = function() {
  var selectElement = document.getElementById("select-element-id");
  selectElement.selectedIndex = 1;
}