Starting with Nodejs

Installing Nodejs

Download the required installer base on your OS and follow the guide :

After installing Nodejs now you can test your Nodejs

> node -v
v12.16.1

The Nodejs package manager (npm) is distributed with Nodejs so it can be test also

> npm -v
v6.14.8

It looks good and now you can ‘play’ a little bit with Nodejs by Hello example.

1. Create file helloWorld.js and put the text below to this file.

//Load HTTP module
const http = require("http");
const host = '127.0.0.1';
const port = 3000;

//Create HTTP server and listen on port 3000 for requests
const server = http.createServer((req, res) => {
//Set the response HTTP header with HTTP status and Content type
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World\n');
});
//listen for request on port 3000
server.listen(port, host, () => {
  console.log(`Server running at http://${host}:${port}/`);
});

2. Go into the same directory as your helloWorld.js file and run:

> node helloWorld.js
Server running at http://127.0.0.1:3000/

3. Open your browser and go to http://localhost:3000/ , you will see the text Hello World

NPM (Node package manager)

NPM is the important tool for working with Nodejs. NPM is used to fetch packages (JavaScript libraries) that needs for development.

Normally, we handle the dependencies by a plain-text definition file named package.json. This file includes all the dependencies, the package’s name, version, description, initial file to execute, production dependencies, development dependencies, versions of Node etc. You should put all the things that NPM needs to fetch and run your application to package.json file

How to add dependencies

Here is the steps to use NPM to download a package, save it into the project dependencies, and then require it in a Node application.

Step 1: create a directory and navigate into it

> mkdir example
> cd example

Step 2: use the npm init command to generate a package.json file (use all default setting)

> npm init
This utility will walk you through creating a package.json file.
It only covers the most common items, and tries to guess sensible defaults.

See `npm help init` for definitive documentation on these fields
and exactly what they do.

Use `npm install <pkg>` afterwards to install a package and
save it as a dependency in the package.json file.

Press ^C at any time to quit.
package name: (example)
version: (1.0.0)
description:
entry point: (index.js)
test command:
git repository:
keywords:
author:
license: (ISC)
About to write to /xxx/xxx/xxx/example/package.json:

{
  "name": "example",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC"
}


Is this OK? (yes) yes

Now you can see there is a package.json file in the example directory

{
  "name": "example",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC"
}

Step 3: install Express and save it in the dependencies list of your package.json file

> npm install express
npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN example@1.0.0 No description
npm WARN example@1.0.0 No repository field.

+ express@4.17.1
added 50 packages from 37 contributors and audited 50 packages in 9.963s
found 0 vulnerabilities

now back to your package.json file and you can see Express is added to the dependencies

{
  "name": "example",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.17.1"
  }
}

Step 4: use Express library by require() function.

You can create file index.js file in the root of example directory and put the content below inside.

const express = require('express')
const app = express();
const port = 8000;

app.get('/', (req, res) => {
  res.send('Hello Express!')
});

app.listen(port, () => {
  console.log(`Example app listening on port ${port}!`)
});

Step 5: start the server

> node index.js
Example app listening on port 8000!

Open browser using url http://127.0.0.1:8000 and you’ll see Hello Express!

Development dependencies

If a dependency is only used for development, you should only save it as a “development dependency” (so it is not included in production). For example, to use the Linting tool eslint :

> npm install eslint --save-dev
npm WARN example@1.0.0 No description
npm WARN example@1.0.0 No repository field.

+ eslint@7.21.0
added 114 packages from 65 contributors and audited 164 packages in 18.901s

13 packages are looking for funding
  run `npm fund` for details

found 0 vulnerabilities

Now back to your  package.json file and you can see these lines is put in the file

  "devDependencies": {
    "eslint": "^7.21.0"
  }

How to run tasks

Beside defining and fetching dependencies, you can also define named scripts in your package.json files and call NPM to execute them with the run-script command.

For example, to define a script to run the eslint development dependency that we install in previous section we might add the following script block to our package.json file (assuming that our application source is in a folder /src/js):

"scripts": {
  ...
  "lint": "eslint src/js"
  ...
}

You be able to run eslint using NPM by calling:

> npm run-script lint

This is all for a simple Nodejs tutorial 😀