Reset shiny fileInput object (see SO question http://stackoverflow.com/questions/17352086/how-can-i-update-an-shiny-fileinput-object)

server.R

shinyServer(function(input, output, session) {

  observe({
    input$btn
    session$sendCustomMessage(type = "resetFileInputHandler", "file1")  
  })
  
})

ui.R

shinyUI(bootstrapPage(
  
  fileInput('file1', 'Choose File'),
  actionButton("btn", "Trigger server to reset file input"),
  
  tags$script('
    Shiny.addCustomMessageHandler("resetFileInputHandler", function(x) {      
        var id = "#" + x + "_progress";
        var idBar = id + " .bar";
        $(id).css("visibility", "hidden");
        $(idBar).css("width", "0%");
    });
  ')
))

Also see:
https://groups.google.com/forum/?fromgroups=#!topic/shiny-discuss/z-KqaNamFCY

Hello,
thanks for this trick! I was using it for a while, but now it's not working with Shiny 0.14, since they are using different upload button style.