javascript - Materialise - 如何在多重选择中动态选择选项？

Question

我有一个多重选择元素，我想动态选择选项的混合，如下所示:

我能够动态选择一个选项，但仅此而已，

document.getElementById('update_days_of_the_week').selectedIndex = 2;
document.getElementById('update_days_of_the_week').selectedIndex = 3;

<div class="row">
  <div class="input-field col s4">
    <select id="update_days_of_the_week" multiple>
      <option value="" disabled selected>Choose your days of the week</option>
      <option value="Monday">Monday</option>
      <option value="Tuesday">Tuesday</option>
      <option value="Wednesday">Wednesday</option>
      <option value="Thursday">Thursday</option>
      <option value="Friday">Friday</option>
      <option value="Saturday">Saturday</option>
      <option value="Sunday">Sunday</option>
    </select>
    <label>Days of the week</label>
  </div>
</div>

上面的代码，显然只选择了索引3，因为selectedIndex = 2被替换了。

Answer 1

使用jQuery你可以做这样的事情:

$('#update_days_of_the_week').val(['Monday', 'Friday'])

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.js" integrity="sha256-WpOohJOqMqqyKL9FccASB9O0KwACQJpFTUBLTYOVvVU=" crossorigin="anonymous"></script>
<select id="update_days_of_the_week" multiple>
  <option value="" disabled selected>Choose your days of the week</option>
  <option value="Monday">Monday</option>
  <option value="Tuesday">Tuesday</option>
  <option value="Wednesday">Wednesday</option>
  <option value="Thursday">Thursday</option>
  <option value="Friday">Friday</option>
  <option value="Saturday">Saturday</option>
  <option value="Sunday">Sunday</option>
</select>