Fetch local file data in R/Shiny

Question

Following an idea from from https://github.com/jpowell96/readFilesWithFetch/blob/master/index.html, I'm trying to read data from a .csv file from the 'www' folder but I get only the 'Reading file' line and the data is not shown. I tried with full path too in fetch (fetch(file:///C:/.../www/this_data.csv')) but got the same results.

Any idea to make it work? (Currently working in Windows but eventually will port it to shinyapps.io.)

Many thanks

  library(shiny)
  library(shinyjs)
  ui <- fluidPage(
    useShinyjs(),

      tags$div(
       tags$html("Reading file"),

       tags$script("
         fetch('./www/this_data.csv')
          .then(response => response.text()) 
          .then(csvString => {
         // Split the csv into rows
         const rows = csvString.split('\n');
         for (row of rows) {
           // Split the row into each of the comma separated values
           console.log(row.split(','));
         }
       });
       ")
    )
  )
  server <- function(input, output, session) {}
  shinyApp(ui, server)

This is this_data.csv:

Date,Open,High,Low,Close
1/2/2007,50.03978,50.11778,49.95041,50.11778
1/3/2007,50.2305,50.42188,50.2305,50.39767
1/4/2007,50.42096,50.42096,50.26414,50.33236
1/5/2007,50.37347,50.37347,50.22103,50.33459
1/6/2007,50.24433,50.24433,50.11121,50.18112
1/9/2007,49.99489,49.99489,49.80454,49.91333
1/10/2007,49.91228,50.13053,49.91228,49.97246
1/11/2007,49.88529,50.2391,49.88529,50.2391

Answer 1

1. You need to save your app file to app.R, exactly this name.
2. In the same folder as the app file, create a www folder and add your csv to that www folder.
3. When you reference it from js, get rid off the www prefix. Every path inside www will be relative path. e.g. you have a www/myfile.txt, it will be just myfile.txt, or if you have another subfolder, www/sub1/file2.csv, it will be sub2/file2.csv.
4. You need to use HTML function to wrap and escape your js code, some symbols like > have special meanings in HTML.
5. No need of shinyjs.

Full code:

library(shiny)
ui <- fluidPage(
    tags$div(
        tags$html("Reading file"),
        tags$script(HTML("
         fetch('this_data.csv')
          .then(response => response.text())
          .then(csvString => {
         // Split the csv into rows
         const rows = csvString.split('\\n');
         for (row of rows) {
         // Split the row into each of the comma separated values
           console.log(row.split(','));
         }
       });
       "))
    )
)
server <- function(input, output, session) {}
shinyApp(ui, server)

If you did all of these, you will see: