I commonly see Search Engine Optimization (SEO) consultants recommend that you render your page on the backend, so that web crawlers can see a lot of nice HTML code that they can then index.
SEO vs. React: Web Crawlers are Smarter Than You Think
Patrick Hund

Yes and they’d be correct. The crawler (Googlebot) only sees HTML, it doesn’t do anything with JavaScript. The indexer, on the other hand (which Google calls its Caffeine infrastructure) is what renders JavaScript. You’re obviously confusing crawling and indexing in this article, thinking they’re the same thing. They’re most definitely not.