js设置select显示值

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

<script>
  // 设置显示值为"Option 2"
  document.getElementById('mySelect').value = '2';
</script>

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

<script>
  // 设置显示值为第二个选项"Option 2"
  document.getElementById('mySelect').selectedIndex = 1;
</script>

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

<script>
  function setSelectedByText(selectId, text) {
    var select = document.getElementById(selectId);
    for (var i = 0; i < select.options.length; i++) {
      if (select.options[i].text === text) {
        select.selectedIndex = i;
        break;
      }
    }
  }

  // 设置显示值为"Option 2"
  setSelectedByText('mySelect', 'Option 2');
</script>

window.onload = function() {
  document.getElementById('mySelect').value = '2';
};

var select = document.getElementById('mySelect');
var newOption = document.createElement('option');
newOption.value = '4';
newOption.text = 'Option 4';
select.appendChild(newOption);

// 确保添加完选项后再设置值
select.value = '4';