The core of the Shiny application is the reactive engine, which tells Shiny when to execute each component. We are now familiar with the reactive flow of various components. Reactive observers have a flag that indicates whether they have been invalidated. Whenever the values of the input object change, all of the descendants in that graph are invalidated. Such invalidated observers are also called dirty or clean. Along with this, the arrows in the flow diagram that have been followed are removed.
Let's discuss an example of a single reactive source and endpoint:
server<- function(input, output) {
output$Plot_output<- renderPlot({
hist(rnorm(input$User_input))
})
}
The flow diagram is as follows:
As soon as the input values change, all the descendants are invalidated and a flush event is triggered:
...
