node.js

History of Javascript

  • 1995 - Javascript in Netscape browser
  • 2005 - AJAX based applications (Gmail)
  • 2008 - Google Chrome with V8 engine
  • 2009 - nodejs

What is node.js?

  • environment for running Javascript
  • doesn't need browser
  • using V8

Install node

https://nodejs.org/en/

Hello world

  • create file index.js with Javascript code
  • execute file using: node index.js 
console.log('Hello world');

Let's get serious...

  • create new folder (mkdir my-app; cd my-app)
  • initialize node package: 
    • npm init
  • it creates package.json file which contains
    • basic package info (author, licence, repository url, etc.)
    • dependencies
    • scripts

 

{
  "name": "my-package",
  "version": "1.0.0",
  "description": "This is just description of my awesome package",
  "main": "index.js",
  "scripts": {
    "dev": "nodemon --exec npm run start",
    "start": "tsc && node dist/index.js",
    "test": "mocha --opts mocha.opts"
  },
  "author": "Martin Nuc",
  "license": "ISC",
  "dependencies": {
    "@types/chai": "4.0.4",
    "@types/mocha": "2.2.43",
    "@types/node": "8.0.28",
    "@types/sinon": "2.3.4",
    "chai": "4.1.2",
    "mocha": "3.5.3",
    "nodemon": "1.12.1",
    "sinon": "3.2.1",
    "ts-node": "3.3.0",
    "typescript": "2.5.2"
  }
}

package.json

Wait, what was that

npm

??

Node package manager

  • when you want to use a code written by someone else
  • packaging system
  • large repository (>550k packages)
  • https://www.npmjs.com
npm install lodash

installs lodash library:

Use library in your code

const _ = require('lodash');

const words = _.words('Hello, how are you?');

// ['Hello', 'how', 'are', 'you']
console.log(words);

Dependencies and GIT

  • we don't commit dependencies
  • put node_modules folder in .gitignore
  • npm install to install dependencies
{
  "name": "my-package",
  "version": "1.0.0",
  "description": "This is just description of my awesome package",
  "main": "index.js",
  "scripts": {
    "dev": "nodemon --exec npm run start",
    "start": "tsc && node dist/index.js",
    "test": "mocha --opts mocha.opts"
  },
  "author": "Martin Nuc",
  "license": "ISC",
  "dependencies": {
    "@types/chai": "4.0.4",
    "@types/mocha": "2.2.43",
    "@types/node": "8.0.28",
    "@types/sinon": "2.3.4",
    "lodash": "4.17.5",
    "chai": "4.1.2",
    "mocha": "3.5.3",
    "nodemon": "1.12.1",
    "sinon": "3.2.1",
    "ts-node": "3.3.0",
    "typescript": "2.5.2"
  }
}

package.json

Semantic versioning

6.11.2

patch

minor version

major version

Semantic versioning

6.11.2

patch

minor version

major version

- major changes, breaks API

Semantic versioning

6.11.2

patch

minor version

- new features

- doesn't break API

major version

- major changes, breaks API

Semantic versioning

6.11.2

patch

- only bugfixes

minor version

- new features

- doesn't break API

major version

- major changes, breaks API

Locking dependencies versions

  • exact version
    • 4.1.2 = only 4.1.2
  • ^ variable minor version
    • ^4.1.2 = 4.1.2, 4.1.3, 4.2.0, 4.2.1...
  • ~ variable patch version
    • ~4.1.2 = 4.1.2, 4.1.3, 4.1.4...
  • try it out: https://semver.npmjs.com

Use lodash

  • install lodash library (https://lodash.com)
  • use camelCase function from lodash to convert your full name to the camel case

Scripts


"scripts": {
  "dev": "nodemon --exec npm run start",
  "start": "node index.js",
  "test": "mocha --opts mocha.opts"
},
  • used to execute commands
  • npm dependencies executables resolution (from node_modules/.bin/*)

npm run <name>

Shortcut for start and test scripts only. For others you have to use npm run

Runs any script from npm.

npm start

npm test

👉

Create your script

  • create script called start for running your app

Global package

  • available in your whole system
  • sudo npm install -g benny-hill
  • use them wisely

Read and write files

require('fs')

  • https://nodejs.org/api/fs.html
  • synchronous vs asynchronous functions

Write file

const fs = require('fs');

fs.writeFileSync('file.txt', 'Hello');

Read file

const fs = require('fs');

let content;
content = fs.readFileSync('file.txt', 'utf8');

Let's try it out !

Asynchronous functions

  • eg. fs.writeFileSync(...) becomes fs.writeFile(..., callback)
  • does not block
  • callbacks
  • 1st callback argument is usually error
const fs = require('fs');

fs.readFile('file.txt', 'utf8', (err, content) => {
    console.log('reading done', content);
});

Try it yourself :-)

  • rewrite previous task in async manner
    • create file with some text
    • read it

Modules

Modules to split app

  • every file may export something:
    • module.exports = function sayHello() {...}
  • use it in another file:
    • const sayHello = require('./file');
    • sayHello()
       
  • export anything - number, object...
    • module.exports = 3.14;
    • module.exports = { ... };
  • alias exports

Export multiple things

  • export
    • exports.sayHello = function sayHello() {...}
    • exports.PI = 3.14;
  • import it elsewhere:
    • const sayHi = require('./file').sayHello;
    • const PI = require('./file').PI;
    • sayHi()

Try it!

  • design functions for synchronous operations:
    • reading file
    • writing file
  • save them in separate file
  • call them from your index.js 
function write(filename, content) {...}
function read(filename) {...}

nodemon

  • makes development easier
  • automatically reruns your code after change
  • npm install nodemon --save-dev
  • just run: nodemon

Create grep

  • searches through files in current directory
  • prints filename, line number and line itself where searched string is found
  • npm start, npm run dev
  • Challenge mode: search through subdirectories
index.js:2 const searchedString = 'devDependencies';
package.json:11   "devDependencies": {

Hints:

- look in documentation for fs.readdir()

- look in docs for fs.stat()

Output when searching for "devDependencies":

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