selecting text by ignoring inner Elements of div tag javascript

<html>
<body>
<script language="javascript">
function getSelectionHTML()
{
    var div = document.getElementById("myDiv");

    if (document.createRange) { 
        var textNode=div.firstChild;
        var rangeObj=document.createRange();
        rangeObj.setStart(textNode,0);
        rangeObj.setEnd(textNode,5);
        div .innerHTML = div .innerHTML.replace(rangeObj.toString(), '<span style="background-color: lime">'+rangeObj.toString()+'</span>')
    }
}
</script>
<div id="myDiv">
asdf as<b>dfas df asf asdf sdfjk  dvh a sjkh jhcdjkv</b> iof scjahjkv ahsjv hdjk biud fcsvjksdhf k

</div>
<form name="aform">
<input type="button" value="Get selection" onclick="getSelectionHTML()">
</body>
</html>

Ok. Let me explain -> getSelectionHTML() method is for selection of characters from 0 to 10. I am getting the values by "myDiv" id. but inner bold, italic & other tags are giving me trouble.

In simple words, I just want to make selection of first ten characters (& apply them span tag) which are in "myDiv" tag.

What exactly I am missing?

Solution

You're trying to select e.g. character 1 to 10 of your text. But when using Range.setStart and .endStart, the first parameter is the text node containing your text. If you browse through the DOM with Firebug (or Web Inspector), you'll notice that character 10 of your text resides in another element (the <b> element), with its own text node.

BTW, you left out several required elements/tags, which can also be a source of errors.

My corrected version reads

<!DOCTYPE html>
<html>
<head>
  <title>Title element is required</title>
<body>
<script>
function getSelectionHTML()
{
    var div = document.getElementById("myDiv");
    var bEl = document.getElementById("bEl");

    if (document.createRange) {.
        var textNode=div.firstChild;
        var rangeObj=document.createRange();
        rangeObj.setStart(textNode,0);
        rangeObj.setEnd(bEl.firstChild,2);
        alert(rangeObj.toString());
//        div.innerHTML = div.innerHTML.replace(rangeObj.toString(), '<span style="background-color: lime">'+rangeObj.toString()+'</span>');
    }
}
</script>
<div id="myDiv">
asdf as<b id="bEl">dfas df asf asdf sdfjk  dvh a sjkh jhcdjkv</b> iof scjahjkv ahsjv hdjk biud fcsvjksdhf k
</div>
<form name="aform">
  <input type="button" value="Get selection" onclick="getSelectionHTML()">
</form>
</body>
</html>

Now rangeObj contains the selected text, but you can't simply insert a <span> element the way you tried, because elements can't be nested this way:

<span>asdf as<b>dfa</span>s df asf…