property selectionEnd

This property returns the index of the character in the edit field of where the currently selected text ends. If there is no selection the property returns 0.

function DoesEditHaveSelection(editBx)
{
    var hasSel = false;
    if (editBx)
    {
        var startPos = editBx.selectionStart;
        var endPos   = editBx.selectionEnd;

        hasSel = (startPos == 0) && (endPos == 0);
    }

    return hasSel;
}