If on the other hand, you have one of those “legacy” applications that has “customers” and makes “money,” and for some reason your boss is not into the idea of you spending a few weeks rewriting the whole front end in React, but you still want in on that declarative React goodness, you may have to figure out how to get React to play well with jQuery or something similar.

If jQuery is making DOM changes that React doesn’t know about, some node that gets reused might be in an unexpected state.