Stop 'downloadHandler` from executing in an ifelse statement - r

Question

I am creating an app where the users can download the plot displayed. I want the user to be able to click download and ShinyAlert will pop up to ask for filename as the input.
So far the file gets downloaded if I press on save. However, when the CancelButton is clicked, shiny tries to download the page's HTML, with a "Failed - Server problem".
I placed an if function inside downloadHandler so that when input$shinyalert != FALSE the downloadHandler will execute the code, but I couldn't find the fault in my code. Any help will be appreciated, thanks.
Here is the code:
UI:
ui <- fluidPage(
useShinyalert(),
plotOutput("vmgraph"),
actionButton("downloadPlot", "Download Plot")
useShinyjs(),
## hide the downloadButton and only display actionButton
conditionalPanel(
"false",
downloadButton("downloadData")
)
)
Server:
observeEvent(input$downloadPlot, {
shinyalert("Save as:",
type = "input",
size = "m",
closeOnEsc = TRUE,
closeOnClickOutside = TRUE,
showConfirmButton = TRUE,
showCancelButton = TRUE,
confirmButtonText = "Save",
confirmButtonCol = "#0075B8",
animation = TRUE)
})
output$downloadData <- downloadHandler(
filename = function() {
if (input$shinyalert != FALSE) {
paste(input$shinyalert, ".png", sep = "")}},
content = function(file) {
if (input$shinyalert != FALSE) {
ggsave(file, plot = vmgraph(), width = 12, height = 7.7)
}})
observeEvent(input$shinyalert, {
## Click on the downloadButton when input$shinyalert is updated
shinyjs::runjs("$('#downloadData')[0].click();")
})

Answer 1

Perform your check for the cancel button before you get into the downloadHandler:
library(shiny)
library(shinyjs)
library(shinyalert)
library(ggplot2)
gg <- ggplot(mtcars, aes(mpg)) +
geom_boxplot()
ui <- fluidPage(
useShinyalert(),
plotOutput("vmgraph"),
actionButton("downloadPlot", "Download Plot"),
useShinyjs(),
## hide the downloadButton and only display actionButton
conditionalPanel(
"false",
downloadButton("downloadData")
)
)
server <- function(input, output) {
observeEvent(input$downloadPlot, {
shinyalert("Save as:",
type = "input",
size = "m",
closeOnEsc = TRUE,
closeOnClickOutside = TRUE,
showConfirmButton = TRUE,
showCancelButton = TRUE,
confirmButtonText = "Save",
confirmButtonCol = "#0075B8",
animation = TRUE
)
})
output$downloadData <- downloadHandler(
# do not perform check here
filename = function() {
paste(input$shinyalert, ".png", sep = "")
},
content = function(file) {
ggsave(file, plot = gg, width = 12, height = 7.7)
}
)
observeEvent(input$shinyalert, {
## Click on the downloadButton when input$shinyalert is updated
# perform the check here
if (input$shinyalert != FALSE) {
shinyjs::runjs("$('#downloadData')[0].click();")
}
})
}
shinyApp(ui = ui, server = server)