在两个ListBoxes中都选择了项目时启用按钮

<select id="listBox1" multiple>
  <option value="item1">项目1</option>
  <option value="item2">项目2</option>
  <option value="item3">项目3</option>
</select>

<select id="listBox2" multiple>
  <option value="item4">项目4</option>
  <option value="item5">项目5</option>
  <option value="item6">项目6</option>
</select>

<button id="myButton" disabled>启用按钮</button>

const listBox1 = document.getElementById('listBox1');
const listBox2 = document.getElementById('listBox2');
const myButton = document.getElementById('myButton');

function checkSelection() {
  const selectedItems1 = listBox1.selectedOptions;
  const selectedItems2 = listBox2.selectedOptions;

  if (selectedItems1.length > 0 && selectedItems2.length > 0) {
    myButton.disabled = false;
  } else {
    myButton.disabled = true;
  }
}

listBox1.addEventListener('change', checkSelection);
listBox2.addEventListener('change', checkSelection);