在js文件中写el表达式取不到值的原因及解决方法

$(document).ready(function() {
      var schoolId=$(‘#jcSchoolSelect option:selected‘).val();
      if(schoolId!=null && schoolId!= ‘‘){
           loadClassSelect(schoolId);
      }
});
function loadClassSelect(schoolId){
      $.ajax({
           url:‘${ctx}/jc/jcClass/findBySchoolId?jcSchool.id=‘+schoolId,
           type:"get",
           async: false,
           success: function (data) {
               $("#jcClassSelect").html("");
               $("#jcClassSelect").get(0).options.add(new  Option(" ",""));
               $.each(data, function(index, value){
                    $("#jcClassSelect").get(0).options.add(new  Option(value.name,value.id));
                });
               $("#jcClassSelect option").each(function(){
                     var value=$(this).val();
                     if (value==jcClassId){
                         $(this).prop("selected", ‘selected‘);
                     }
                });
          }
　　})
};