How to listen for more than one event expression within a Shiny observeEvent

This should do it, note that you still have to check if the buttons were clicked as mentioned by @MrFlick

1. You can use reactive expression

#rm(list = ls())
library(shiny)
ui <- shinyUI(bootstrapPage(
  actionButton("test1", "test1"),
  actionButton("test2", "test2"))
)

server <- shinyServer(function(input, output) {

  toListen <- reactive({
    list(input$test1,input$test2)
  })
  observeEvent(toListen(), {
    if(input$test1==0 && input$test2==0){
      return()
    }
    print('Hello World')
  })
})

shinyApp(ui, server)

2. As per example given by @MrFlick (now deleted)

#rm(list = ls())
library(shiny)
ui <- shinyUI(bootstrapPage(
  actionButton("test1", "test1"),
  actionButton("test2", "test2"))
)

server <- shinyServer(function(input, output) {

  observeEvent(input$test1 | input$test2, {
    if(input$test1==0 && input$test2==0){
      return()
    }
    print('Hello World')
  })
})

shinyApp(ui, server)

Using the | operator in the observeEvent() eventExpr won't work if the inputs are not numeric, logical or complex types.

For example, notice the message at the end of running this simple Shiny app with an actionButton() and a selectInput() used inside the observeEvent() eventExpr:

library(shiny)

ui <- shinyUI(bootstrapPage(
  selectInput("test1", "test1", choices = c("a", "b")),
  actionButton("test2", "test2"))
)

server <- shinyServer(function(input, output) {
  
  observeEvent(input$test1 | input$test2,
  {
    print('Hello World')
  })
})

shinyApp(ui, server)
#> 
#> Listening on http://127.0.0.1:6563
#> Warning: Error in |: operations are possible only for numeric, logical or
#> complex types

^{Created on 2022-04-02 by the reprex package (v2.0.1)}

Instead, you can create a vector of the inputs inside the observeEvent() and include ignoreInit = TRUE if you wish to not print "Hello World" on app initialization. This approach accommodates any input types.

library(shiny)
ui <- shinyUI(bootstrapPage(
  selectInput("test1", "test1", choices = c("a", "b")),
  actionButton("test2", "test2"))
)

server <- shinyServer(function(input, output) {
  
  observeEvent(ignoreInit = TRUE, c(
    input$test1,
    input$test2
  ),
  {
    print('Hello World')
  })
})

shinyApp(ui, server)

---

If the observeEvent(c(input$a, input$b), {...}) approach doesn't float your boat, then I can recommend the reactive({list(input$a, input$b}) approach which goes like this:

library(shiny)
ui <- shinyUI(bootstrapPage(
  selectInput("test1", "test1", choices = c("a", "b")),
  actionButton("test2", "test2"))
)

server <- shinyServer(function(input, output) {
  
  event_trigger <- reactive({
    list(input$test1, input$test2)
  })
  
  observeEvent(ignoreInit = TRUE, event_trigger(),
  {
    print('Hello World')
  })
})

shinyApp(ui, server)

This approach has the advantage of being portable, meaning you can use it as the eventExpr for multiple observeEvent() calls (or other listeners) if needed.