I have built a selection of ASP.net controls on my default.aspx page. I am using the following line of javascript to try and get the value of an ASP control.

var imgUrl = document.getElementById("<%= backUrl.ClientID %>").value;

However this throws up the following error when I try to run my app on SP.

Sorry, there was a problem with bannerSlide. For support, please contact the developer. An error occurred during the processing of /sites/dev/bannerSlide/Pages/test.aspx. Code blocks are not allowed in this file.

Most online solutions seem to point towards modifying a web file but I don't think this is possible with SharePoint Online (Office 365).

Any help would be greatly appreciated, thanks.

1 Answer 1


Default.aspx is a Site Page and inline C# or VB code is not allowed in Site Pages. So you need to replace the code block (i.e. <%= backUrl.ClientID %>) with the literal id of the element.

  • You can use inline code even in site pages as long as the page is not customized, e.g. it has been deployed through a farm solution package. As soon as you edit it in Designer it will break. Still, this is no help to Ben for SP Online.
    – Louis
    Sep 26, 2013 at 0:10

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