Filewatcher nodejs

const events = require("events"),
  util = require("util");

const fs = require("fs"),
  watchDir = "./watch",
  processedDir = "./done";
  
  /*Let's extend events.EventEmitter in order to be able
  to emit and listen for event*/
  
  class Watcher extends events.EventEmitter {
  constructor(watchDir, processedDir) {
    super();
    this.watchDir = watchDir;
    this.processedDir = processedDir;
  }

/* Cycles through directory and process any file
found emitting a process event for each one*/

  watch() {
    const watcher = this;
    fs.readdir(this.watchDir, function(err, files) {
      if (err) throw err;
      for (let index in files) {
        watcher.emit("process", files[index]);
      }
    });
  }

/* Start the directory monitoring 
leveraging Node's fs.watchFile */

  start() {
    var watcher = this;
    fs.watchFile(watchDir, function() {
      watcher.watch();
    });
  }
}
 
 /* Let's instantiate our Watcher object 
 passing to the constructor our folders path */
 
let watcher = new Watcher(watchDir, processedDir);


/*Let's use the on method inherited from 
event emitter class to listen for process 
events and move files from source folder 
to destination*/

watcher.on("process", function process(file) {
  const watchFile = this.watchDir + "/" + file;
  const processedFile = this.processedDir + "/" + file.toLowerCase();
  fs.rename(watchFile, processedFile, function(err) {
    if (err) throw err;
  });
});

/*Start it!!!*/

watcher.start();

Source: codementor.io

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