Определение размера файла

const { stat, writeFile } = require('fs');
 
 
const filesize = 1; // magick number
function generateFileName() {
  // magick generation of file name
  return 'file.txt'; 
}
function getContent() {
  // magick function to get content
  return 'bla bla bla';
}
 
function sleep(ms) { // magick function to immitate loop
  return new Promise((resolve) => setTimeout(resolve, ms));
}
 
 
 
function getFileSize(name) { // function to return file size
  return new Promise((resolve, reject) => stat(name, (err, { size }) => {
    if (err) return reject(err);
    resolve(size);
  }));
}
function writeFileContent(name, content) { // function to write content to file
  return new Promise((resolve, reject) => writeFile(name, content, (err) => {
    if(err) return reject(err);
    resolve();
  }));
}
 
(async function main(fileName) {
  const cfs = await getFileSize(fileName);
  if(cfs > filesize) { // magick calculation if filesize is greater than magick number
     return main(generateFileName());
  }
  const content = getContent(); // just magick..
  await writeFileContent(fileName, content);
 
  // magick immitation of loop
  await sleep(200);
  return main(fileName);
})(generateFileName()).catch(console.error);