replace - jQuery surround highlighted text with SPAN

Question

The following code is supposed to surround the highlighted text in a given Div with a span.

$(document).ready(function(){
    $('.format').click(function(){
       var highlight = window.getSelection();

        var spn = '<span class="highlight">' + highlight + '</span>';
        $('.conttext').content().replace(highlight, spn);

    });
});

A function of this nature could be used to provide formating options to an HTML contenteditable DIV.

Something is clearly wrong though as it does not currently work.

http://jsfiddle.net/BGKSN/20/

Answer 1

DEMO: http://jsfiddle.net/BGKSN/24/

$(document).ready(function(){
    $('.format').click(function(){
        var highlight = window.getSelection();  
        var spn = '<span class="highlight">' + highlight + '</span>';
        var text = $('.conttext').text();
        $('.conttext').html(text.replace(highlight, spn));
    });
});

Later Edit:

Based on the comment, this is the real functional example:

http://jsfiddle.net/BGKSN/40/

$(document).ready(function(){
    $('.format').click(function(){
        var highlight = window.getSelection(),  
        spn = '<span class="highlight">' + highlight + '</span>',
        text = $('.conttext').text(),
        range = highlight.getRangeAt(0),
        startText = text.substring(0, range.startOffset), 
        endText = text.substring(range.endOffset, text.length);

        $('.conttext').html(startText + spn + endText);
    });
});

Docs: https://developer.mozilla.org/en-US/docs/Web/API/window.getSelection