lesson2

Lesson 2: Basics

Let's look at Node.js fundamentals and develop simple applications.

How Node.js is Different from JavaScript?

Let's take a look at the main difference between Node.js and JavaScript.

Node'js and browser JavaScript differ when it comes to globals.

Node.js Global Objects

These objects are available in all modules. As a global, they are always available to Node.js applications without using require().

• console
• __filename
• __dirname

console.log(__filename);
console.log(__dirname);

Node.js Process Information

Each Node.js script that runs is, in essence, a process. Conveniently, developers can access useful information in code with the process object.

> process.pid
50169
> process.cwd()
'/Users/1002139/ltcs/nodejs-course'

ps |grep node outputs all Ndoe.js programs running on your machine.

$ ps |grep node
50169 ttys000    0:00.12 node
50581 ttys001    0:00.00 grep node

process.argv

The process.argv property returns an array containing the command line arguments passed when the Node.js process was launched.

• The 1st element: the absolute pathname of the executable that started the Node.js process
• The 2nd element: the path to the JavaScript file being executed
• The remaining elements: any additional command line arguments

Write process-args.js

// print process.argv
process.argv.forEach((val, index) => {
  console.log(`${index}: ${val}`);
});

Test

$ node process-args.js one two=three four
0: /usr/local/bin/node
1: /Users/mjr/work/node/process-2.js
2: one
3: two=three
4: four

Exporting and Importing Modules

There is no way to include modules using JavaScript itself in browsers. Scripts are supposed to be linked together using a different language(HTML).

We can export and import modules in Node.js with great dependency management. We'll cover this in a different lesson in more detail.

Command Line Application

Write a command line application which prints a greeting message on the console.

greeting.js

function getFullName(first, last, country) {
  var eastCountries = ['KR', 'CH', 'JP'];
  var westContrries = ['US', 'CA', 'UK'];
  country = country.toUpperCase();

  if (eastCountries.indexOf(country) > -1) {
    return last + ' ' + first;
  } else if (westContrries.indexOf(country) > -1) {
    return first + ' ' + last;
  } else {
    throw new Error('Invalid country!');
  }
}

var first = process.argv[2];
var last = process.argv[3];
var country = process.argv[4];

console.log('Hello, ' + getFullName(first, last, country) + '!');

Test

$ node greeting.js Dale Seo KR
Hello, Seo Dale!
$ node greeting.js Dale Seo US
Hello, Dale Seo!

Server Application

Don't worry if the details in this lesson seem over your head.

I'd like to give you a preview of what you'll be able to do when you've completed the course.

What is HTTP Server?

HTTP server listens or waits for requests from clients and returns responses.

Develop Our First HTTP Server

Our first server always respons with "Hello World".

1. Import Required Module

Use the require directive to load the http module and store the returned HTTP instance into an http variable.

var http = require('http');

2. Create Server

Use the created http instance and call http.createServer() method to create a server instance. It accepts a single argument, a callback function, that will be called on each HTTP request received by the server. This callback function recevies, as arguments, the request and response objects, which are commonly shortened to req and res.

var server = http.createServer(function(req, res) {
   res.end('Hello, World!'); // End the response with the message, "Hello, World!"
});

For every HTTP request received by the server, the callback funtion will be invoked with new req and res objects.

3. Listen to client for incoming requests

Bind the server instance at port 3000 using the listen method associated with the server instance.

server.listen(3000);

4. Test Our First HTTP Server

Execute the helloServer.js to start our first HTTP server.

$ node helloServer.js
Server running at http://localhost:3000

Open http://localhost:3000 in any browser and observe the result. You should receive a plain-text page consisting of the words "Hellow, World!".

Or use the curl command on the terminal

$ curl http://localhost:3000
Hello, World!

Now, we have our first HTTP server up and running which is responding to all the HTTP requests at port 3000.

Challenges

• Calculator
• Counter Server