how to get selection inside a div using jquery/javascript

This is slightly verbose because of long-winded boundary comparisons and because IE takes a different approach from other browsers, but does the job in all major browsers. It also handles multiple selections in Firefox.

jsFiddle: http://jsfiddle.net/Q982A/2/

Code:

function getSelectedTextWithin(el) {
    var selectedText = "";
    if (typeof window.getSelection != "undefined") {
        var sel = window.getSelection(), rangeCount;
        if ( (rangeCount = sel.rangeCount) > 0 ) {
            var range = document.createRange();
            for (var i = 0, selRange; i < rangeCount; ++i) {
                range.selectNodeContents(el);
                selRange = sel.getRangeAt(i);
                if (selRange.compareBoundaryPoints(range.START_TO_END, range) == 1 && selRange.compareBoundaryPoints(range.END_TO_START, range) == -1) {
                    if (selRange.compareBoundaryPoints(range.START_TO_START, range) == 1) {
                        range.setStart(selRange.startContainer, selRange.startOffset);
                    }
                    if (selRange.compareBoundaryPoints(range.END_TO_END, range) == -1) {
                        range.setEnd(selRange.endContainer, selRange.endOffset);
                    }
                    selectedText += range.toString();
                }
            }
        }
    } else if (typeof document.selection != "undefined" && document.selection.type == "Text") {
        var selTextRange = document.selection.createRange();
        var textRange = selTextRange.duplicate();
        textRange.moveToElementText(el);
        if (selTextRange.compareEndPoints("EndToStart", textRange) == 1 && selTextRange.compareEndPoints("StartToEnd", textRange) == -1) {
            if (selTextRange.compareEndPoints("StartToStart", textRange) == 1) {
                textRange.setEndPoint("StartToStart", selTextRange);
            }
            if (selTextRange.compareEndPoints("EndToEnd", textRange) == -1) {
                textRange.setEndPoint("EndToEnd", selTextRange);
            }
            selectedText = textRange.text;
        }
    }
    return selectedText;
}

Alternatively, you could use my Rangy library, and the code becomes:

function getSelectedTextWithin(el) {
    var selectedText = "";
    var sel = rangy.getSelection(), rangeCount = sel.rangeCount;
    var range = rangy.createRange();
    range.selectNodeContents(el);
    for (var i = 0; i < rangeCount; ++i) {
        selectedText += sel.getRangeAt(i).intersection(range);
    }
    return selectedText;
}