js获取option选定的值

<select id="mySelect">
  <option value="1">Option 1</option>
  <option value="2">Option 2</option>
  <option value="3">Option 3</option>
</select>

// 获取select元素
var selectElement = document.getElementById('mySelect');

// 获取选定的值
var selectedValue = selectElement.options[selectElement.selectedIndex].value;

console.log(selectedValue); // 输出选定的值

document.getElementById('mySelect').addEventListener('change', function() {
  var selectedValue = this.options[this.selectedIndex].value;
  console.log(selectedValue);
});

window.onload = function() {
  var selectElement = document.getElementById('mySelect');
  if (selectElement) {
    console.log(selectElement.options[selectElement.selectedIndex].value);
  }
};