如何在javascript中选择多个中添加选定项

我想帮助你。单击“自我选项”时，我已选择了要为选项属性添加的多个选择框

                <select multiple  name="system" class="form-control system">
                    <option value="Windows"> Windows </option>
                    <option value="Linux">  Linux </option>
                    <option value="MacOS"> MacOS </option>
                    <option value="FreeBSD"> FreeBSD </option>
                </select>

窗户
Linux
马科斯
FreeBSD

在要选择的选项中使用选定属性

selected

示例：让您选择Windows和MacOS

<select multiple  name="system" class="form-control system">
  <option value="Windows" selected> Windows </option>
  <option value="Linux">  Linux </option>
  <option value="MacOS" selected> MacOS </option>
  <option value="FreeBSD"> FreeBSD </option>
</select>

<select multiple  name="system" class="form-control system">
  <option value="Windows" selected> Windows </option>
  <option value="Linux">  Linux </option>
  <option value="MacOS" selected> MacOS </option>
  <option value="FreeBSD"> FreeBSD </option>
</select>

---

在要选择的选项中使用选定属性

selected

示例：让您选择Windows和MacOS

<select multiple  name="system" class="form-control system">
  <option value="Windows" selected> Windows </option>
  <option value="Linux">  Linux </option>
  <option value="MacOS" selected> MacOS </option>
  <option value="FreeBSD"> FreeBSD </option>
</select>

<select multiple  name="system" class="form-control system">
  <option value="Windows" selected> Windows </option>
  <option value="Linux">  Linux </option>
  <option value="MacOS" selected> MacOS </option>
  <option value="FreeBSD"> FreeBSD </option>
</select>

现在从

javascript

中获取选项，并进行如下检查

getElementsByClassName("o1").selected = true;
getElementsByClassName("o2").selected = true;

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我认为改进后的答案会有所帮助。@issaalhadithi请参阅jQuery的更新代码。我建议您保留一些其他属性来选择元素，可以是任何类或id。尽量避免使用选择器和值