When do we call it engineering and when do we call it research?

There is not a clear line but I’d say the context matters.

An academic computer scientist produces conference papers about a program they wrote, not a program. Such a person might be wary of doing a live demo at that conference because… things could go wrong. Some CS grad students and profs are brilliant programmers, but not all of them. To write a paper about a program you only need to get the program sorta-kinda working, it doesn’t need to be reliable or have any polish.

A software developer writes programs for a living, it is secondary if they present about them. Such a program has to be good enough for people to really use. The software dev isn’t afraid to do a live demo because they have used the program every day for six months.

In the case of React somebody could have made a prototype and written about it and that would have been research but if you got it packaged up so anybody could use it… that’s engineering.

Even the very quotidian applications programming I do sometimes has an aspect of research; for instance I was working on a query system that is a hybrid of full text and boolean search and discovered a way to write a parser that corrects any mistakes a user types, e.g. if it is

  (A AND B

it gets rewritten to

  A AND B

there was some reading compiler books (without the answer I wanted but a mention of a COBOL compiler from the 1970s that did this) and a lot of thinking about parser theory and drawing illustrations on paper. Out of all that came a product that customers are using everyday.