Been there, seen that.

I some months ago, they asked me to join a new team because they needed help with React and, although my main technology is RoR, I quite like JavaScript.

What I found is that the last developer shoved 2500 lines React, Redux and Typescript in a Rails application just to make a sortable and filterable table!! Apparently, after perpetrating this atrocity, he updated his resumée and found a job in another company.

I really think that it is good to have a grumpy senior developer in each team stopping those things from happening.