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

#jfriend00 solution is correct. However, In the above solution. It never cleans the timeout. It may cause an issue. If u need blocking code and better timer handling u can use setInterval.
Sample:
const checkTime = 1000;
var fs = require("fs");
const messageFile = "test.js";
const timerId = setInterval(() => {
const isExists = fs.existsSync(messageFile, 'utf8')
if(isExists) {
// do something here
clearInterval(timerId)
}
}, checkTime)
You can also run your python program. No need to write another script.
const spawn = require("child_process").spawn;
const proc = spawn('python',["./watch.py"]);
proc.stdout.on('data', (data) => console.log(data.toString()))
proc.stderr.on('data', (data) => console.log(data.toString()))

Answer 2

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.