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.