I don't even understand the requirement. Do you distrust your users that much? And even then, aren't your users the defacto site owners? If they want to intentionally destroy their own site (it's pretty hard to accidentally insert malicious code), are you really going to be able to prevent that with 100% certainty?Or phrased a different way, if you distrust your users that badly, then why are you giving them the ability to customize the javascript (or worse, server-side code) on the site?
we also have lot of vendor supplied assets which includes htmls, js and others along with translated content which needs to be scanned before being pushed to runtime.