Shiny modules and renderUI passing javascript code

Here is a solution with a MutationObserver. It observes whether there's a change in the container and then it applies slick().

chartTableBoxUI <- function(id) {

  ns <- NS(id)
  div(
    h2(id),
    tags$div(DTOutput(ns("chart"))),
    tags$div(DTOutput(ns("table")))
  )

}

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

  ns <- session$ns

  vals <- reactiveValues()

  observeEvent(input$chart_rows_selected, {
    vals$sel<- input$chart_rows_selected
  }, ignoreNULL = FALSE)

  output$chart <- renderDT({
    datatable(
      mtcars, options = list(dom='t', pageLength = 5), class = "compact stripe"
    )
  })

  output$table <- renderDT({
    datatable(
      mtcars[vals$sel, 1:3], options = list(dom='t'), class = "compact stripe"
    )
  })

}

library(shiny)
library(DT)
library(shinyjs)

js <- "
$(document).ready(function(){
    var container = document.getElementById('tabs');
    // create an observer instance
    var observer = new MutationObserver(function(mutations) {
      setTimeout(function(){
        $('#tables').slick({
          arrows: true,
          dots: true
        });
      }, 0);
    });
    // observe 
    observer.observe(container, {subtree: false, childList: true});
});
"
ui <- fluidPage(

  fluidRow(
    tags$head(
      tags$link(rel="stylesheet", type="text/css",
                href="https://cdnjs.cloudflare.com/ajax/libs/slick-carousel/1.9.0/slick-theme.css"),
      tags$link(rel="stylesheet", type="text/css",
                href="https://cdnjs.cloudflare.com/ajax/libs/slick-carousel/1.9.0/slick.css"),
      tags$script(type="text/javascript", 
                  src="https://cdnjs.cloudflare.com/ajax/libs/slick-carousel/1.9.0/slick.js"),
      tags$script(HTML(js)),
      tags$style(HTML(
        "#tables .slick-prev {
      position:absolute;
      top:65px; 
      left:-100px;
      }
      #tables .slick-next {
      position:absolute;
      top:95px; 
      left:-100px;
      }
      .slick-prev:before, .slick-next:before { 
      color:red !important;
      }
      .content {
      margin: auto;
      padding: 20px;
      width: 80%;
      }"))
    ),

    sliderInput("dr", "Num of tables:", min = 0, max = 12, value = 2),
    div(style = "margin-top: -60px"),
    uiOutput("tabs")

  )

)

server <- function(input, output, session) {
  for(i in 1:12)
    callModule(chartTableBox, paste0("Table",i))

  output$tabs <- renderUI({
    num_tables <- input$dr
    tags$div(class="content",
             tags$div(id="tables",
                      lapply(paste0("Table",1:num_tables), chartTableBoxUI)
             ))
  })

}

shinyApp(ui, server)