shiny reactive, reactiveValue and eventReactive, observe and observeEvent in Shiny reactive


Example

A reactive can be used to make output depend on another expression. In the example below, the output$text element is dependent on text_reactive, which in turn is dependent on input$user_text. Whenever input$user_text changes, output$text element and text_reactive become invalidated. They are recalculated based on the new value for input$user_text.

library(shiny)

ui <- fluidPage(
  headerPanel("Example reactive"),
  
  mainPanel(
    
    # input field
    textInput("user_text", label = "Enter some text:", placeholder = "Please enter some text."),
    
    # display text output
    textOutput("text"))
)

server <- function(input, output) {
  
  # reactive expression
  text_reactive <- reactive({
    input$user_text
  })
  
  # text output
  output$text <- renderText({
    text_reactive()
  })
}

shinyApp(ui = ui, server = server)