shiny
htmltools
req()
seq()
on.exit()
observe()
isolate
observeEvent
eventReactive
reactiveTimer()
invalidateLater(ms)
git
If a function changes the value of the original object.
f(y1)
Then the copy also get changed.
y2
## <Y> ## Public: ## a: 2 ## b: 2 ## clone: function (deep = FALSE)