Set CKeditor First letter Cap's Using Jquey KeyUp

 $(document).ready(function () 
{ 
  CKEDITOR.on('instanceCreated', function (e) {
     e.editor.on('contentDom', function () {  
      e.editor.document.on('keyup', function (event) {
 if (this.selectionStart == 0 && event.data.$.keyCode >= 65 && event.data.$.keyCode <= 90 && !(event.data.$.shiftKey) && !(event.data.$.ctrlKey) && !(event.data.$.metaKey) && !(event.data.$.altKey)) 
{ 
var $t = $(this);
 event.data.$.preventDefault();
 var char = String.fromCharCode(event.data.$.keyCode);
 $t.val(char + $t.val().slice(this.selectionEnd));
 this.setSelectionRange(1,1); 
} 
});
 });

and aspx code is:

  ID="CKEditor1" BasePath="~/ckeditor/" runat="server" Width="940px" Height="400px"> 

here, this.selectionStart is undefined, here how can i call the this.selectionStart ?

TIA