Node.js is an event-driven platform for building scalable network applications. It uses non-blocking I/O and asynchronous calls to handle many connections concurrently without blocking. At the core of Node.js is a single-threaded event loop that processes tasks in the order they are placed into the queue, executing callbacks asynchronously without blocking the main thread. The event loop handles all incoming requests and passes them to the JavaScript engine to execute callbacks and return responses. Node.js uses the V8 JavaScript engine and runs built-in modules and third-party modules for common tasks like HTTP servers and file system access.

1. Node.js quick intro

2. Node.js
Platform for scalable network applications
servers and clients
Uses event driven, non-blocking I/O
epoll, kqueue, /dev/poll, or select
process never blocks, no deadlocks
internal event loop

3. Event driven platform
Non-blocking - not waiting for things to finish
Uses asynchronous platform-specific API’s
“Single-threaded” - sequential task execution
Runs synchronous API’s in threads

4. Node.js architecture
Based on V8
JavaScript Virtual
Machine (engine)
+ standard library
Google Chrome uses
V8 too

5. Event loop illustration
// event loop
while (true) {
lock (queue) {
var tickEvents = copy(queue);
queue.empty();
}
for (var i = 0; i < tickEvents.length; i++) {
InvokeJSFunction(tickEvents[i]);
}
}
// thread-safe event pushing
lock (queue) {
queue.push(event);
}
// io call
fs.readFile(“pwd”, function(e, d){
console.log(“file data:”, d);
});

6. Callbacks
var fs = require(“fs”);
var cb = function(err, data){
if (err) throw err;
console.log(“File contents: ” + data);
}
fs.readFile(“pwd1”, cb);
fs.readFile(“pwd2”, cb);

7. Http server app
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello Worldn');
}).listen(1337, "127.0.0.1");

8. Node.js launching
$ echo ‘console.log(“hey there”)’ | node
$ node app.js

9. Workers event loop

10. That was quick Node.js introduction
Thanks