Basic form-submission shiny app used in "Persistent data storage in shiny apps" article http://deanattali.com/blog/shiny-persistent-data-storage/

app.R

library(shiny)

# Define the fields we want to save from the form
fields <- c("name", "used_shiny", "r_num_years")

# Save a response
# ---- This is one of the two functions we will change for every storage type ----
saveData <- function(data) {
  data <- as.data.frame(t(data))
  if (exists("responses")) {
    responses <<- rbind(responses, data)
  } else {
    responses <<- data
  }
}

# Load all previous responses
# ---- This is one of the two functions we will change for every storage type ----
loadData <- function() {
  if (exists("responses")) {
    responses
  }
}

# Shiny app with 3 fields that the user can submit data for
shinyApp(
  ui = fluidPage(
    DT::dataTableOutput("responses", width = 300), tags$hr(),
    textInput("name", "Name", ""),
    checkboxInput("used_shiny", "I've built a Shiny app in R before", FALSE),
    sliderInput("r_num_years", "Number of years using R", 0, 25, 2, ticks = FALSE),
    actionButton("submit", "Submit")
  ),
  server = function(input, output, session) {
    
    # Whenever a field is filled, aggregate all form data
    formData <- reactive({
      data <- sapply(fields, function(x) input[[x]])
      data
    })
    
    # When the Submit button is clicked, save the form data
    observeEvent(input$submit, {
      saveData(formData())
    })
    
    # Show the previous responses
    # (update with current response when Submit is clicked)
    output$responses <- DT::renderDataTable({
      input$submit
      loadData()
    })     
  }
)

Hi Dean,
can you explain how the bubbling trigger of the submit button is listened to and caught in the code chunk of rendering responses?
Why does the input$submit appear in the renderDataTable part? I would rather see this as better suited case for another orberveEvent.

    output$responses <- DT::renderDataTable({
      input$submit #when this is not here, the app wont render responses, however the event listening is not explicitly defined at this point
      loadData()
}) 

Also the formData seems not to be executed when the inputs stay the same, is it because of lazy loading? I figure this by adding a print statement to the formData code:

    formData <- reactive({
      print("formData executed")
      data <- sapply(fields, function(x) input[[x]])
      data
    })

I think there a some internals hidden to my sight I would like to understand.

I'm using the same code but all my entries are NULL when the Submit Button is clicked. Any thoughts as to why this might happen?