Lets say your software as a service website has a real time analytics graph, so that customers can look at statistics of how much they are using the service in real time.

One potential question a customer might want to know is "How many API calls have I made over the last hour". This is a moving window average question, and it needs to be displayed/done on the front end.

My company that I work at has such a feature.

Algorithms questions come up all the time in javascript development.

I can cite examples from the front-end I'm working on right now, but that wouldn't sound like a fair example (it's an AVR debugger). But all sophisticated applications are complicated in their own ways, and most of them require developers who can actually, you know, program.

Even if all you're doing is CRUD, how much computer science is embedded in even a straightforward framework like React? "Lots", is I think the answer.