D365 lookup Custom filtering javascript

 In my case, I need to add custom filtering when I select a lookup it will populate another lookup. when the user will click on the search icon it will show only filter data. 

I was following: https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/clientapi/reference/controls/addpresearch

sample code:

 var demoLAB = demoLAB || {};   
 var classId;   
  demoLAB.Stuedent = {   
   Form: {   
    Load: function (executionContext) {   
     'use strict';   
     var formContext = executionContext.getFormContext();       
     this.attachEvents(executionContext);   
    },   
    attachEvents: function (executionContext) {   
     'use strict';   
     var formContext = executionContext.getFormContext();   
     var form = demoLAB.Stuedent.Form;       
     // Student Change Event   
     formContext.getAttribute("demo_studentId").addOnChange(form.studentOnChange);       
     
    },   
    studentOnChange: function (executionContext) {   
     'use strict';   
     var formContext = executionContext.getFormContext();   
     var form = demoLAB.Stuedent.Form;   
     if (formContext.getAttribute("demo_studentId").getValue() != null) {   
      var studentId = formContext.getAttribute("demo_studentId").getValue()[0].id.slice(1, -1);   
      // Retrive current student current class   
      Xrm.WebApi.retrieveRecord("student", studentId, "?$select=_classId_value").then(   
       function success(studentResult) {   
        classId = studentResult._classId_value;   
        // Add presearch for teacher    
        formContext.getControl("demo_teacherId").addPreSearch(form.filterTeacher);   
       },   
       function (error) {   
       }   
      );   
     }   
    },   
    // Call back function for teacher    
    filterTeacher: function (executionContext) {   
     'use strict';   
     var formContext = executionContext.getFormContext();   
     var teacherFilter = "<filter type='and'><condition attribute='demo_classId' operator='eq' value='" + classId + "'/></filter>";   
     formContext.getControl("demo_teacherId").addCustomFilter(teacherFilter, "teacher");   
    },         
   }   
  };