Use future-promise to improve R/Shiny user experience

 https://rstudio.github.io/promises/articles/shiny.html

https://rstudio.github.io/promises/articles/overview.html

https://rstudio.github.io/promises/articles/casestudy.html

 https://engineering-shiny.org/optimizing-shiny-code.html#asynchronous-in-shiny