How to highlight selected text in IE 11

I have a prototype JS snippet here :- 
if (document.selection) {
            // IE 8, 9, 10
            var range = document.selection.createRange();
            selectedText = range.text;
            selectionOK = this.highlightSelection(range);
            this.getOffset();
} else if (document.getSelection) {
   // IE 11 support see "http://msdn.microsoft.com/en-in/library/ie/ms535869(v=vs.85).aspx#properties"
            var range = document.getSelection().getRangeAt(0);
            selectedText = range.toString();
            //selectedText = document.getSelection();
            selectionOK = this.highlightSelection(range.createRange());
highlightSelection() is my custom function that accepts TxtRange and uses execCommand() to highlight the selected text.
Now I am not able to convert range object to TxtRange and consequently, not able to highlight selected text in IE 11.

how to get TxtRange in IE 11 ?