There is no ctl00_icerikcontainer_slider
in your page. It looks like a server-assigned id so I think your <span id="icerikcontainer_slider">
should be <span runat="server" id="icerikcontainer_slider">
and then you could use
var e = document.getElementById('<%=icerikcontainer_slider.ClientID %>').innerHTML;
You can find more info about ASP.Net inline expressions at http://weblogs.asp.net/ahmedmoosa/archive/2010/10/06/embedded-code-and-inline-server-tags.aspx