How to limit the number of characters accepted by textInput in Shiny app

Question

I would like my Shiny app (in R) to limit the number of characters a user can input in response to a textInput command.

I can request the user to limit to 50 characters and can have the app send him a message if he does not, but it would be better if he were prevented from overrunning the limit in the first place.

Suggestions appreciated.

Answer 1

For example by using shinyBS and stringr packages:

library(stringr)
library(shinyBS)
string <- "Destrier ipsum dolor cold weirwood, consectetur adipisicing elit, sed full of terrors incididunt green dreams always pays his debts. Ut in his cups sandsilk, no foe may pass spearwife nisi ut aliquip we do not sow. Duis aute warrior feed it to the goats death before disgrace maidenhead dog the seven pariatur. Rouse me not cupidatat non proident, suckling pig culpa qui officia deserunt mollit we light the way."

    observe({
        if(str_length(string)>50) {
          newstring <-str_sub(string, end=50)
          createAlert(session, inputID = "alert_anchor",
            message = "You exceeded 50 character limit!",
            dismiss = TRUE,
            block = FALSE
            append = TRUE)
            updateTextInput(session, inputID, value = newstring)
    }

    })

    # remember to create alert to shiny UI
    # bsAlert(inputID = "alert_anchor")

Demo page for shinyBS:ShinyBS

Answer 2

You can't add custom attribute to textInput, you could probably be able to write custom function to generate input, but it will be easier to do this in javascript:

shinyjs::runjs("$('#inputName').attr('maxlength', 50)")