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In our previous experiment we showed how Surfly’s proxy technology could be used to change the behaviour of any website on the fly. However, that was just a tip of the iceberg, and this time we will get to some more fun stuff.

One of the things you can do with a sandboxing proxy is injecting custom Javascript code into the pages. Many client-side browser extensions make use of this simple, yet very powerful concept. One great advantage when using a proxy is that you don’t have to install any additional software on the client side.

To demonstrate the possibilities of this technique, we’ve created a simple app inspired by services such as Genius and AnnotatorJS. This app can add annotation functionality to any web page, and the source code is available here.

The button below will open a session to Wikipedia, enhanced with annotation functionality. You can read other people’s comments and add you own.

Note that this app is only made for demonstration purposes, so it might be unstable at times, and the annotations will be removed once in a while.
You will also need an up-to-date browser (Google Chrome, Firefox, or Safari is recommended).

The ability to inject custom Javascript code into the pages is a very powerful tool. It provides a flexible framework for changing the original behaviour of web apps, or for enhancing them with new features. In combination with a sandboxing proxy, it is possible without changing the original code, or installing any software on the client side.

Surfly’s proxy is capable for even more advanced functionality. Since it has access to the raw HTTP traffic, it can do things that are impossible for browser extensions. Stay tuned for our future Surfly Labs experiments!

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