Wait until file is created to read it in node.js

Question

I am trying to use file creation and deletion as a method of data transfer (not the best way, I know.) between python and nodejs. The python side of the program works fine, as I am quite familiar with python 3, but I can't get the node.js script to work.

I've tried various methods of detecting when a file is created, mainly with the use of try {} catch {}, but none of them have worked.

function fufillRequest(data) {
  fs.writeFile('Response.txt', data)
}

while(true) {
  try {
    fs.readFile('Request.txt', function(err,data) {
      console.log(data);
    });
  } catch {

  }
}

The program is supposed to see that the file has been created, read it's contents, delete it and then create and write to a response file.

Answer 1

You can either user a recurring timer or fs.watch() to monitor when the file appears.

Here's what it would look like with a recurring timer:

const checkTime = 1000;
const fs = require('fs');

function check() {
   setTimeout(() => {
       fs.readFile('Request.txt', 'utf8', function(err, data) {
          if (err) {
              // got error reading the file, call check() again
              check();
          } else {
              // we have the file contents here, so do something with it
              // can delete the source file too
          }
       });
   }, checkTime)
}

check();

Note: Whatever process is creating this file should probably use an exclusive access mode when writing so that you don't create a race condition where it starts reading before the other process is done writing.