Custom Javascript problem not working

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1

I am trying to implement custom javascript problem. I have my javascript application.
But when I submit my problem it shows “Could not grade your answer. The submission was aborted.”
Here code

 <h2>Is causal relationship explicitly stated in the statement?</h2>
 <label class="container">Yes
 <input type="radio" name="radio" id="checkBox" onclick="func.showQue()">
 <span class="checkmark-1"></span>
 </label>
 <label class="container">No
 <input type="radio" name="radio" onclick="func.showQue()">
 <span class="checkmark-1"></span>
 </label>

 <div style="display: none;" id="question">
 <h2>If yes, which is the cause?  </h2>
 <label class="container">Supreme court declares the statute unenforceable 
 <input type="radio" name="final" id="checkbox2">
 <span class="checkmark-2"></span>
 </label>
 <label class="container">He goes free
 <input type="radio" name="final">
 <span class="checkmark-2"></span>
 </label>
 </div>

<script>
    let func = (function() {
      function showQue() {
      let checkBox = document.getElementById("checkBox");
      let text = document.getElementById("question");
      if (checkBox.checked == true){
      text.style.display = "block";
      } else {
       text.style.display = "none";
      }
      }

      function getGrade() {
           let checkans = document.getElementById("checkbox")
           let check2ans = document.getElementById("checkbox2")

           if (checkans.checked == true){
               if (check2ans.checked == true) {
                   return JSON.stringify("correct")
               }
          } else {
          /   return JSON.stringify("wrong")
           }

   
      }

      state = {
        choice: "correct"
      }

      function getState() {
        return JSON.stringify(state);
      }

      return {
          showQue: showQue,
          getGrade: getGrade,
          getState: getState
      }
    })();
</script>

and the problem “cms-modules.2b7ffc378730.js:175 Uncaught TypeError: Cannot read property ‘getGrade’ of undefined”. Not sure what I am missing.

and code from edx

  <problem>
  <script type="loncapa/python">
  import json
  def all_true(exp, ans):
  response = json.loads(ans)
  return response["answer"] == "correct"
   </script>
     <customresponse cfn="all_true">
     <jsinput gradefn="func.getGrade"
      height="500"
      html_file="/static/inputjs.html"
      title="iframe Title"
      sop="true"/>
    </customresponse>
    </problem>