下面是我的HTML和Javascript。我用的是百里香。我只想对这个选择标签执行模糊操作，即对用户选择的值进行模糊警告。
$(document).ready(function(){
alert("called");
});
});
function addSubject(){
var x = document.getElementById("sub").value;
alert(x);
}<body>
<div class="form-group" style="margin-top: 10px;">
<label th:text="'Subject'"></label>
<select class="form-control" id="sub" th:onblur="'addSubject()'">
<option value="" th:disabled="disabled" th:selected="selected" th:text="'Select Subject'"></option>
<option th:text="'Add New Subject'" th:value="addSub"></option>
<option th:each="freesub : ${detailsofexams}"
th:text="${#strings.capitalize(freesub)}"
th:value="${#strings.toUpperCase(freesub)}">
</option>
</select>
</div>
<script
th:src="@{${@mvcResourceUrlProvider.getForLookupPath('/admin/dist/js/freecontent.js')}}"></script>
</body>他们在我的JS文件中出现了打字错误，正如@Simon sir在第一条评论中所建议的那样，我的代码开始工作。以下是正确的代码
$(document).ready(function(){
alert("called");
});
function addSubject(){
alert("x");
}<div class="form-group" style="margin-top: 10px;">
<label th:text="'Subject'"></label>
<select class="form-control" id="sub" th:onblur="'addSubject()'">
<option value="" th:disabled="disabled" th:selected="selected" th:text="'Select Subject'"></option>
<option th:text="'Add New Subject'" th:value="addSub"></option>
<option th:each="freesub : ${detailsofexams}"
th:text="${#strings.capitalize(freesub)}"
th:value="${#strings.toUpperCase(freesub)}">
</option>
</select>
</div>