waitForFileToExist.js

const
  path = require('path'),
  fs = require('fs');

const waitForFileToExist = (filepath, forTime = 5000) => {
  return new Promise((resolve, reject) => {
    const
      filedir = path.dirname(filepath),
      filename = path.basename(filepath);
    if (fs.existsSync(filepath)) {
      resolve(true);
    } else {
      let watcher;
      const timer = setTimeout(() => {
        watcher.close();
        reject(`${filename} does not exist`)
      }, forTime);
      watcher = fs.watch(filedir, function (event, who) {
        if (event === 'rename' && who === filename) {
          if (fs.existsSync(filepath)) {
            watcher.close();
            clearTimeout(timer);
            resolve(true);
          } else {
            watcher.close();
            clearTimeout(timer);
            reject(`${filename} does not exist`)
          }
        }
      })
    }
  })
}

waitForFileToExist('a.txt').then((doesFileExist) => {
  console.log(doesFileExist);
})