Introduction to Node.js

Nodejs Background

Node.js was first introduced to the community at JS-EU conference in 2009 by its creator Ryan Dhal. He saw the problem with blocking on I/O and how JavaScript was the perfect language for getting mainstream programmers doing asynchronous programming on the server. His presentation was received with a standing ovation.

Ryan Dhal’s presentation speaker profile during JS-EU conf in 2009

Node.js is one of the most popular projects on Github after beating out heavyweights such as Ruby on Rails and jQuery.

Nodes repo on github

Cross Platform

Node.js is cross-platform. It can run on Windows, Unix, and Mac OS X.

NPM (Node Package Manager)

Automatically installed with Node

Commands: npm help | install | ls | search

Packages can be installed locally or globally via -g (useful to use packages as cmdline tools)

Npm install will create a directory ./node_modules/

Nodejs Building Block

An event loop and a low level I/O API call Libuv, Google Chrome’s V8 and custom C++, and JavaScript code developed specifically for the Node.js platform itself. These three things makes up the Nodejs Platform.

Event Loop

The event loop is what allows Node.js to perform non-blocking I/O operation even though JavaScript is single threaded by offloading operations to the system kernel (the core of the OS). When one of these operations completes, the kernel tells Node.js that the appropriate callback may be added to the poll queue to eventually be executed.

When Node.js Starts

process.nextTick()

Event loop structure

Consists of phases. Each phase has a FIFO (first in first out) queue of callbacks to execute.

On each phase, Node.js runs any operations specific to that phase, then runs callbacks in that phase’s queue until empty queue or max num of callbacks are executed then moves to the next phase.

Since any operations may schedule more operations and new events processed in the poll phase are queued by the kernel, poll events can be queued while polling events are being processed.

Between each run of the event loop, Node.js checks if it is waiting for any asynchronous I/O or timers and shuts down cleanly if there are not any.

Timers:executes callbacks scheduled by setTimeout() and setInterval() . A timer specifies the threshold after which a provided callback may be executed rather than the exact time a person wants it to be run.

Pending I/O callbacks: executes almost all callbacks with exception of close callbacks, the ones scheduled by timers, and setImmediate .

Idle, prepare:only used internally.

Poll:retrieve new I/O events; Node will block here when appropriate.

Two main functions:

1. Executing scripts for timers whose threshold has elapsed, then
2. Processing events in the poll queue.

Module and Packages

A module is any file or directory that can be loaded by Node.js’ using require() .

A package is a file or directory described by a package.json .

In the Node.js module system, each file is treated as a separate module

// mymodule.js

const anotherModule = require(‘anotherModule’)

console.log(module);

In each module, the module free variable is a reference to the object representing the current module.

When a file is run directly from Node.js, require.main is set to its module. Meaning it is possible to determine whether a file has been run directly by testing require.main===module .

For a file foo.js , this will be true if run via Node foo.js , but false if run by require(‘./foo’) because the module provides a filename property, the entry point of the current app can be obtained by checking require.main.filename .

Core Modules

Core modules are compiled into Node binary distribution and loaded automatically when the Node process starts. Still, these need to be imported in order to be used in your application.

Some core modules: http, url, querystring, path, fs, util.

Node.js in Practice

JavaScript

Typing:dynamic, weak

Multi-paradigm:imperative, object-oriented, functional, event-driven.

Standard:ECMAScript — ES’2015 (ES6): classes, modules, generators, arrow functions, promises.

Influenced by: Java, C, Python.

Primitive types: numbers, strings, boolean, Null, Undefined.

Examples

var x = 10.7; // hoisted at global or function level

const y = “hello”; // block-level scoped

var arr = [1,2,3];

for(var i = 0; i<arr.length; i++) {
  console.log(arr[i]);
}

Learning Path and Resources

To learn Node.js, you need 3 things.

• Knowledge of JavaScript
• Understanding of how server side works
• Node.js

Tutorials

· Learn Node.js — Best Node.js tutorials

· Learn Node JS in a Week via Video Screencast

· NodeSchool

· Felix’s Node.js Guide

· Node Tuts

· Node.js for Beginners

· Thinkful Web Development Bootcamp || Node Skills Course

Books

· The Node Beginner Book

· Mastering Node.js

· Up and Running with Node.js

· Node.js in Action

· Smashing Node.js: JavaScript Everywher

· Node.js & Co. (in German)

· Most detailed list of free JavaScript Books

· Mixu’s Node Book

· Beginning Web Development with Node.js