How to add custom popup to tinymce editor and add fields content to editor

I have added code to open bootstrap modal in tinymce custom button. I tried and added code below whi

ch I have tried. I don’t know why it came blank fields not adding the content.

How can this fixed?

<!DOCTYPE html>
<html lang="en">

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script
   src="https://cdn.tiny.cloud/1/qagffr3pkuv17a8on1afax661irst1hbr4e6tbv888sz91jc/tinymce/5/tinymce.min.js"></script>
<link href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css" rel="stylesheet"
   integrity="sha384-QWTKZyjpPEjISv5WaRU9OFeRpok6YctnYmDr5pNlyT2bRjXh0JMhjY6hW+ALEwIH" crossorigin="anonymous">
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js"
   integrity="sha384-YvpcrYf0tY3lHB60NNkmXc5s9fDVZLESaAA55NDzOxhy9GkcIdslK1eN7N6jIeHz" crossorigin="anonymous"></script>
<script>
   tinymce.init({
      selector: '#editor',
      plugins: 'autolink image link lists code template',
      toolbar: 'undo redo | bold italic strikethrough forecolor backcolor | image link bullist numlist custom_button code',
      menubar: false,
      height: 'calc(100vh - 2rem)',
      setup: (editor) => {
         editor.ui.registry.addButton('custom_button', {
            icon: 'comment-add',
            tooltip: 'Insert Sharequote',
            onAction: function (api) {
               $('#exampleModal').modal('show');
            }
         });
      },
   });

   $(document).on('click', '.saveChanges', function () {
      var editor = tinymce.get('editor');
      editor.execCommand('mceInsertTemplate', false, `
                        <h1>${$('#heading').html()}</h1>
                        <p>${$('#content').html()}</p>
                  `);
   });

</script>
<textarea id="editor"></textarea>
<div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel"
   aria-hidden="true">
   <div class="modal-dialog" role="document">
      <div class="modal-content">
         <div class="modal-header">
            <h5 class="modal-title" id="exampleModalLabel">Modal title</h5>
         </div>
         <div class="modal-body">
            <input type="text" class="form-control" id="heading" />
            <textarea id="content" class="form-control"></textarea>
         </div>
         <div class="modal-footer">
            <button type="button" class="btn btn-primary saveChanges">Save changes</button>
         </div>
      </div>
   </div>
</div>
</html>