Do search engines love JavaScript generated content?

Question

Search Engine Optimization

The question/doubt came up while learning GatsbyJS (but the question is common to everything in JS, like React). After all, if JS generates the text of the page ("I will sell a moped") - then this text is not in the downloaded HTML and it is more difficult for the search engine to guess what the page is about and give it out when searching.

On the site gatsbyjs they write that it is very friendly with search engines, but it really looks like self-promotion and I have doubts...

Well, yes, you can put the necessary keywords in the HEAD section on the page. You can even populate the ld+json section. But the content itself - in which cases will it be indexed, and in which not? (For example, the text of a story or even a blog post cannot be inserted entirely into HEAD, but you want it to be indexed). And search engines value such content from JS more than pure HTML content or lower?

And Google and Yandex execute js code from the page? And what are the limitations of the sandbox (requirements for JS code)? For example, if the /bands/metallica page code is almost the same as /bands/mango-mango, and downloads information about the band from the server via the API, will both search engines turn to the API? Should the code work quickly (otherwise it will be slammed by timeout) or almost without restrictions? Are any operations prohibited (for example, accessing the network)?

There are some examples of pages that, for some queries, are on the first SERP pages by content, but at the same time (if you download them with curl) do not contain the words from the query (but generate this text from js). There may be standalone blogs of programmers / admins on gatsby / react that are found in the texts of the posts.

Answer 1

Alibaba seems to be not the biggest fools. They make statics and pick up dynamics from above. And Google, in my opinion, said that 5 seconds is enough for everyone. That is, you have to render the page pretty quickly, and then SEOs often advise a prerender