Shiny updateTextInput between modules by passing the session object in between

shiny_updateTextInput_module.R

library(shiny)

# MODULES ----------------------------------------------------------------------
text_ui <- function(id) {
  ns <- shiny::NS(id)
  shiny::tagList(
    textInput(ns("text"), "Write here"),
    verbatimTextOutput(ns("display"))
  )
}

text_server <- function(input, output, session) {
  rv.text <- reactiveValues(val = FALSE)
  
  observeEvent(input$text, {
    rv.text$val <- input$text
  })
  
  output$display <- renderText({
    rv.text$val
  })
  
  return({ session })
}

reset_btn_ui <- function(id) {
  ns <- shiny::NS(id)
  shiny::tagList(
    actionButton(ns("reset"), "Reset")
  )
}

reset_btn_server <- function(input, output, session, TextModuleSession) {
  observeEvent(input$reset, {
    updateTextInput(session = TextModuleSession, "text", value = "")
  })
}

# MAIN -------------------------------------------------------------------------
ui <- fluidPage(
  fluidRow(
    column(6,
           text_ui("text"),
           reset_btn_ui("btn")
    )
  )
)

server <- function(input, output, session) {
  TextModuleSession <- callModule(module = text_server,
                                  id = "text")
  
  callModule(module = reset_btn_server,
             id = "btn",
             TextModuleSession)
  
}

# Shiny update and reset input with Shiny modules
# Related source: https://stackoverflow.com/a/51757792/
shinyApp(ui, server)