find actual text start and end position of a selected text, even with childNodes present.

text_selection_with_childNodes.js

    var offset = 0;
    var selection = window.getSelection();
    var range = selection.getRangeAt(0);
    var start = range.startOffset;
    var end = range.endOffset;

    if ( selection.baseNode.parentNode.hasChildNodes() ) { 
        for ( var i = 0 ; selection.baseNode.parentNode.childNodes.length > i ; i++ ) { 
            var cnode = selection.baseNode.parentNode.childNodes[i];
            if (cnode.nodeType == document.TEXT_NODE) {
                if ( (offset + cnode.length) > start) {
                    break;
                }   
                offset = offset + cnode.length;
            }   
            if (cnode.nodeType == document.ELEMENT_NODE) {
                if ( (offset + cnode.textContent.length) > start) {
                    break;
                }   
                offset = offset + cnode.textContent.length;
            }   
        }   
    }   

    start = start + offset;
    end = end + offset;