const fs = require('fs').promises;

const EventEmitter = require('events');

class FileWatcher extends EventEmitter {

constructor(file, delay) {

super();

this.timeModified = undefined;

this.file = file;

this.delay = delay;

this.watchTimer = undefined;

}

startWatch() {

if (!this.watchTimer) {

this.watchTimer = setInterval(() => {

fs.stat(this.file).then((stat) => {

if (this.timeModified !== stat.mtime.toString()) {

fs.readFile(this.file, 'utf-8').then((content) => {

this.emit('change', content);

}).catch((error) => {

this.emit('error', error);

});

this.timeModified = stat.mtime.toString();

}

}).catch((error) => {

this.emit('error', error);

});

}, this.delay);

}

}

stopWatch() {

if (this.watchTimer) {

clearInterval(this.watchTimer);

this.watchTimer = undefined;

}

}

}

const watcher = new FileWatcher('test.txt', 1000);

watcher.on('error', console.error);

watcher.on('change', (change) => {

console.log('new change:', change);

});

watcher.startWatch();