Javascript 自动选择下拉菜单不选择

Question

我正在编写一个网站，我希望 select 自动设置所有下拉菜单，而不是手动操作。问题是我的 JS 代码带来了值，但它没有 select 任何选项所以框保持像 "Select an option"

HTML:

 <tr> <td>Gender</td> <td> <div class="select2-container select2-container-active" id="s2id_ContentPlaceHolder1_personDetails_genderDropDownList"> <a href="javascript:void(0)" class="select2-choice select2-default" tabindex="-1"> <span class="select2-chosen" id="select2-chosen-2">Select an Option</span> <abbr class="select2-search-choice-close"></abbr> <span class="select2-arrow" role="presentation"> <b role="presentation"></b></span></a><label for="s2id_autogen2" class="select2-offscreen"></label> <input class="select2-focusser select2-offscreen" type="text" aria-haspopup="true" role="button" aria-labelledby="select2-chosen-2" id="s2id_autogen2" tabindex="0" autocomplete="Female"></div> <select name="_ctl0:ContentPlaceHolder1:personDetails:genderDropDownList" id="ContentPlaceHolder1_personDetails_genderDropDownList" onchange="nzis.UpdateDropdownErrorLabel(this)" errorlabel="mandatory" tabindex="-1" title="" style="display: none;"> <option selected="selected" value=""></option> <option value="M">Male</option> <option value="F">Female</option> </select> </td> </tr>

JavaScript:

var index = document.getElementById('s2id_ContentPlaceHolder1_personDetails_genderDropDownList).selectedIndex; alert("value="+document.getElementById('s2id_ContentPlaceHolder1_personDetails_genderDropDownList').value); alert("text="+document.getElementById('s2id_ContentPlaceHolder1_personDetails_genderDropDownList').options[1].text); s2id_autogen1.value= document.getElementById('s2id_ContentPlaceHolder1_personDetails_genderDropDownList').options[2].text; s2id_autogen1.checked = true; var index = document.getElementById('s2id_ContentPlaceHolder1_personDetails_genderDropDownList').selectedIndex; alert("value="+document.getElementById('s2id_ContentPlaceHolder1_personDetails_genderDropDownList').value); alert("text="+document.getElementById('s2id_ContentPlaceHolder1_personDetails_genderDropDownList').options[1].text); s2id_autogen2.value= document.getElementById('s2id_ContentPlaceHolder1_personDetails_genderDropDownList').options[2].text;

有什么建议吗？ :)

非常感谢！

Answer 1

您似乎没有 ID 为 ContentPlaceHolder1_personDetails_titleDropDownList 的元素，因此无法使用 document.getElementById 获取该元素，因此您很可能会收到错误 Uncaught TypeError: Cannot read property 'selectedIndex' of null你的主机。

编辑：您是要使用 s2id_ContentPlaceHolder1_personDetails_genderDropDownList 作为您的选择器吗？

Javascript 自动选择下拉菜单不选择

Javascript autoselect for dropdown not selecting

javascript

html

select

option