compare observeEvent to observe plus isolate in a shiny app

gistfile1.txt

# oberveEvent includes the ability of the first parameter to be an expression. But if the return value of that expression is 
# null, the ignore null setting blocks updates, even though other parts of the expression are updating.
# in the example below with the default settings, button Event1 will only trigger the update of "observeEvent either button"
# after Event2 has been pushed at least once

library(shiny)

# Define UI for application that draws a histogram
ui <- fluidPage(

    # Application title
    titlePanel("Observers"),

           actionButton("event1", "Event 1"),
           actionButton("event2", "Event 2"),
           p("reactiveout",verbatimTextOutput("reactiveout", placeholder = TRUE)),
           p("setWithinReactive",verbatimTextOutput("setWithinReactive", placeholder = TRUE)),
           p("observeEvent either button",verbatimTextOutput("observeEventOut", placeholder = TRUE)),
           p("observe either button",verbatimTextOutput("observeOut", placeholder = TRUE)),
           p("buttonClicked observeEvent",verbatimTextOutput("buttonClicked", placeholder = TRUE))
        
)

# Define server logic required to draw a histogram
server <- function(input, output) {
    observeEvent(input$event1,
                 {
                     resultstr <- paste("button 1", input$event1, input$event2)
                     output$buttonClicked <- renderText({resultstr})
                    })
    observeEvent(input$event2,
                 {
                     resultstr <- paste("button 2", input$event1, input$event2)
                     output$buttonClicked <- renderText({resultstr})
                 })    
    observeEvent({
        input$event1
        input$event2
        },
                 {
                     resultstr <- paste("button 1 or 2", input$event1, input$event2)
                     output$observeEventOut <- renderText({resultstr})
                 })     
 
    observe({
        input$event1
        input$event2
    isolate({
                     resultstr <- paste("observe 1 or 2", input$event1, input$event2)
                     output$observeOut <- renderText({resultstr})
                 })})
    fromreactive <- reactive({
        resultstr <-  paste("button 1 or 2", input$event1, input$event2)
        output$setWithinReactive <- renderText({fromreactive()})
        resultstr
    })
    output$reactiveout <- renderText({fromreactive()})


}

# Run the application 
shinyApp(ui = ui, server = server)