CODEWITHSUNDEEP
javascriptnode.jsevent-loop
overexchange
overexchange

Reputation: 1

How NodeJS event loop works?

For the below code,

var fs = require('fs');

fs.watch('target.txt', function(event, fileName){
    console.log('Event: ' + event + ', for file: ' + fileName);
    });

Console.log('Now watching target.txt');

As per the below architecture,

1) fs.watch() will invoke libuv. libuv will launch a thread to track change event on target.txt. The result from libuv will go to v8 and again through NodeJS Bindings in the form of callback with a buffer having data.

2) libuv adds change event in Event queue. As the event loop picks the change event, corresponding call back is executed in v8 run time.

enter image description here

Is my understanding correct?

Upvotes: 3

Views: 744

Answers (1)

Lajos Arpad
Lajos Arpad

Reputation: 77063

No, you misunderstand it. NodeJS does not have threads, it is single-threaded instead, using the Observer Pattern. The event loop waits for events to occur (to observe an event). When an event is occurred, then it calls its handler. The illusion of multi-threaded approach comes from the fact that Node frequently uses async events, defining callback functions to be executed when a given task is finished. Read more here.

Upvotes: 1

Related Questions