Auto complete and selection of multiple values in text box shiny

Look into shinysky package and textInput.typeahead. You can further customize the style of the textinput yourself. Edit: I added example with select2Input from the shinysky package also for reference

rm(list = ls())

library(shinysky)
library(shiny)

my_autocomplete_list <- c("John Doe","Ash","Ajay sharma","Ken Chong","Will Smith","Neo")

ui <- shinyUI(
  fluidPage(tags$style(type="text/css",".shiny-output-error { visibility: hidden; }",".shiny-output-error:before { visibility: hidden; }"),
            tags$style(type="text/css","#search { top: 50% !important;left: 50% !important;margin-top: -100px !important;margin-left: -250px 
                       !important; color: blue;font-size: 20px;font-style: italic;}"),         

            mainPanel(  
              # one way of doing it
              textInput.typeahead(id="search",
                                  placeholder="Type your name please",
                                  local=data.frame(name=c(my_autocomplete_list)),
                                  valueKey = "name",
                                  tokens=c(1:length(my_autocomplete_list)),
                                  template = HTML("<p class='repo-language'>{{info}}</p> <p class='repo-name'>{{name}}</p>")
              ),
              br(),br(),
              # using select2Input
              select2Input("select2Input1","",choices=c(my_autocomplete_list),type = c("input", "select"))
              )
  )
)

server <- function(input, output, session) {}
shinyApp(ui = ui, server = server)

Edit 2 as per request. Please wrap your objects in a reactive expressions as I did e.g. var <- reactive({...}) so you can re-use those later

rm(list = ls())

library(shinysky)
library(shiny)

my_autocomplete_list <- c("John Doe","Ash","Ajay sharma","Ken Chong","Will Smith","Neo")

ui <- shinyUI(
  fluidPage(sidebarPanel(select2Input("txt","",choices=c("a","b","c"),selected=c("")), br(),actionButton("go","submit"), width =2),
            mainPanel(textOutput('text'))
  )
)

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

  var <- reactive({
    if(input$go==0){return()}
    isolate({
      input$go
      cbind("a","c")
    })
  })  
  output$text <- renderText({var()})
}
shinyApp(ui = ui, server = server)

A much easier approach imho is to use shiny::selectizeInput(). It allows you to autocomplete inputs with via the choices argument.

rm(list = ls())

library(shiny)

my_autocomplete_list <- c("John Doe","Ash","Ajay sharma",
                          "Ken Chong","Will Smith","Neo")

ui <- shinyUI(
  selectizeInput(
    inputId = 'search',
    label = 'Search',
    choices = my_autocomplete_list,
    selected = NULL,
    multiple = TRUE, # allow for multiple inputs
    options = list(create = FALSE) # if TRUE, allows newly created inputs
  )
)

server <- function(input, output, session) {}
shinyApp(ui = ui, server = server)