Find Label Inside Gridview using Javascript

function FetchLabel(button) 
{
     var row = button.parentNode.parentNode;
     var label = GetChildControl(row, "lbl_employee_first_name");
     alert(label.innerHTML);
     return false;
};

function GetChildControl(element, id) 
{
    var child_elements = element.getElementsByTagName("*");
    for (var index = 0; index  <=child_elements.length-1;index ++) 
    {
       if (child_elements[index].id.indexOf(id) != -1) 
       {
           return child_elements[index ];
       }
    }
};

<asp:Button Text="Fetch" runat="server" OnClientClick="return FetchLabel(this);" />
<asp:Label ID="lbl_employee_first_name" runat="server" Text = '<%# Eval("employee_first_name") %>'></asp:Label>