Javascript and User Contents

there are a lot of applications around the web filtering out user contents for scripts. But my question is, have you guys ever experienced a need where a开发者_运维问答llowing javascript in the user input provide rich set of functionalities?

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Apps that need to allow JavaScript input normally make their own version like Facebook did with FBJS.

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Apps where the whole point is to test out some code. Prime example would be jsfiddle: http://jsfiddle.net

Apart from that, no, not really. Even the Facebook case is not really user data. That's API for third party developers, not users. And with third party developers you can easily implement an authentication system for their apps and revoke permission if they break the rules.