fs.FSWatcher in Node.js

fs.FSWatcher is an EventEmitter that is used to watch the changes/updates in a directory. fs.watch() will emit a 'change' event when a file is modified. We will get a better understanding by looking into it's implementation.

 var fs = require('fs');
 var watcher = fs.watch(__dirname);

Here we have assigned a directory that needs to be watched, which means if there are any modifications to be made in this directory the fs.watch() (i.e watcher in our case) function will emit a change event.

watcher.on('change', function name(event, filename){
        // your code here
}); 

OR 

 fs.watch('./tmp', { encoding: 'buffer'}, (eventType, filename) => {
   if(filename){
     // your code here
   }
});

In the example above scenario  we are providing the filename as a buffer other wise filename will be a UTF-8 string.

Hence , FSWatcher is a simple event emitter with convenient stat()/close() methods. Let's take a deeper look now into the close method

 Close():

 watcher.close() 

 
In case you want to stop watching the current being watched file/directory you can call the close()  method which will stop the watcher looking for changes.

Error event:  

In case an error orrcurs while watching the file error event is emitted.

You can also take a look at Node.JS offical document on FSWatcher