Replying to Add-On Index enhancements - #7 by cintiadr here, because the other thread was made with the intention of gsoc discussions on the project.
It’s funny how the smallest of issues sometimes get us(me in this case) stuck 
. The reason for the console error was basically that although the new url pointed to “react-router”, it pointed to “react-router v4.0” whereas our project previously depended on “ReactRouter” which was part of V3.0.2 .
The next question is as to how did this happen in the first place?
The answer to this is that we previously used a url which was dynamic i.e. it gets resolved to a different one .The url used was this. This url basically points to the latest version of react router which is now V4.0 . Now, if we look into the contents of this resolved url , we realise that ReactRouter.min.js no longer exists and that only react-router.js is present. Hence , naturally I didn’t initially think that there’s going to be a difference between the two and created a pull request with a url pointing to react-router.js .
This new file missed some vital code on which our project currently depends and hence the console error . On checking the npm package.json file, I realised that we were using v3.0.2 and when I navigated to the React-router files of v3.0.2, I found the file right there. Hence I have now created an updated PR with the link to the exact same file. I have also tested it locally and can confirm that Add-On Index is back up and running 
.