js添加selected属性

<select id="mySelect">
  <option value="1">Option 1</option>
  <option value="2" selected>Option 2</option> <!-- 默认选中 -->
  <option value="3">Option 3</option>
</select>

// 假设你想选中值为"2"的选项
var selectElement = document.getElementById('mySelect');
var options = selectElement.options;

for (var i = 0; i < options.length; i++) {
  if (options[i].value === '2') {
    options[i].selected = true;
    break;
  }
}

document.querySelector('#mySelect option[value="2"]').selected = true;

// 更改selected属性后
document.querySelector('#mySelect option[value="2"]').selected = true;

// 强制重绘
var dummy = selectElement.offsetHeight; // 读取一个会触发回流的属性