Fallinfo

Start / Terminate

// Starting                  
node app_name.js

// Terminating
process.exit(1)

Environment

process.env.NODE_ENV 
// developmnet

process.env.NODE_ENV = "production"

Arguments

// Passing arguments
node app.js arg_val
(or)
node app.js arg_name=arg_val

// Accessing arguments
const args = process.argv.slice(2)
args[0]
(or)
const args = require('minimist')(process.argv.slice(2))
args['name']
(or)
const args = process.argv.slice(2)
(or)
process.argv.forEach((val, index) => {
  console.log(`${index}: ${val}`)
})

Export / Import

// Type 1
// Exporting
const obj = {
  name_1 : 'val_1',
  name_2 : 'val_3'
}

module.exports = obj

// Importing
const obj = require('./obj')



// Type 2
// Exporting
const obj = {
  name_1 : 'val_1',
  name_2 : 'val_3'
}

exports.obj = obj

// Importing
const items = require('./obj')
items.obj



// Type 3
// Exporting
exports.obj = {
  name_1 : 'val_1',
  name_2 : 'val_3'
}

// Importing
const car = require('./items').obj

package.json

// sample package.json

{
  "name": "test-project",
  "version": "1.0.0",
  "author": {
    "name": "some_name",
    "email": "some_name@whatever.com",
    "url": "https://whatever.com"
  },
  "homepage": "https://whatever.com/package",
  "description": "A package to work with strings",
  "keywords": ["email", "machine learning", "ai"],
  "contributors": ["some_name (https://whatever.com)"],
  "license": "MIT",

  "main": "src/main.js",
  "private": true,

  "bugs": "https://github.com/whatever/package/issues",
  "repository": "github:whatever/testing",

  "scripts": {
    "dev": "webpack-dev-server --inline --progress --config build/webpack.dev.conf.js",
    "start": "npm run dev",
    "unit": "jest --config test/unit/jest.conf.js --coverage",
    "test": "npm run unit",
    "lint": "eslint --ext .js,.vue src test/unit",
    "build": "node build/build.js"
  },

  "dependencies": {
    "vue": "^2.5.2"
  },

  "devDependencies": {
    "autoprefixer": "^7.1.2",
    "babel-core": "^6.22.1"
  },

  "engines": {
    "node": ">= 6.0.0",
    "npm": ">= 3.0.0",
    "yarn": "^0.13.0"
  },

  "browserslist": ["> 1%", "last 2 versions", "not ie <= 8"]
}





* version - indicates the current version
* name - sets the application/package name
* description - is a brief description of the app/package
* main - set the entry point for the application
* private - if set to true prevents the app/package to be accidentally published on npm
* scripts - defines a set of node scripts you can run
* dependencies - sets a list of npm packages installed as dependencies
* devDependencies - sets a list of npm packages installed as development dependencies
* engines - sets which versions of Node.js this package/app works on
* browserslist - is used to tell which browsers (and their versions) you want to support


* ^: It will only do updates that do not change the leftmost non-zero number. 
     If you write ^0.13.0, when running npm update, it can update to 0.13.1, 0.13.2, 
     and so on, but not to 0.14.0 or above. If you write ^1.13.0, when running npm update, 
     it can update to 1.13.1, 1.14.0 and so on, but will not update to 2.0.0 or above.
* ~: if you write ~0.13.0, when running npm update it can update to patch releases: 0.13.1 is ok, 
     but 0.14.0 is not.
* >: you accept any version higher than the one you specify
* >=: you accept any version equal to or higher than the one you specify
* <=: you accept any version equal or lower to the one you specify
* <: you accept any version lower to the one you specify
* =: you accept that exact version
* -: you accept a range of versions. Example: 2.1.0 - 2.6.2
* ||: you combine sets. Example: < 2.1 || > 2.6

Event loop

// Event loop run for every iteration in the call stack

// nextTick run the code at the end of the current iteration
process.nextTick(() => {
  // code
})

// setTimeout/setImmediate run the code as the next iteration
setTimeout(() => {
  // code
}, 0)

(or)

setImmediate(() => {
  // code
})

Event Emitter

// Custom event emitters

const EventEmitter = require('events')
const custom_ev = new EventEmitter()

custom_ev.on('start', () => {
  console.log('started')
})

custom_ev.emit('start')

(or)

custom_ev.on('start', number => {
  console.log(`started ${number}`)
})

custom_ev.emit('start', 23)

(or)

custom_ev.on('start', (start, end) => {
  console.log(`started from ${start} to ${end}`)
})

custom_ev.emit('start', 1, 100)

Http server

// Building server
const http = require('http')

const port = process.env.PORT

const server = http.createServer(function (req, res) {
  res.statusCode = 200
  res.setHeader('Content-Type', 'text/html')
  res.end('Hello, World!')
})

server.listen(port, function () {
  console.log(`Server running at port ${port}`)
})

Http request

// GET
const https = require('https')
const options = {
  hostname: 'whatever.com',
  port: 443,
  path: '/todos',
  method: 'GET'
}

const req = https.request(options, res => {
  console.log(`statusCode: ${res.statusCode}`)

  res.on('data', d => {
    process.stdout.write(d)
  })
})

req.on('error', error => {
  console.error(error)
})

req.end()



// POST
// PUT
// DELETE
const https = require('https')

const data = JSON.stringify({
  todo: 'Buy the milk'
})

const options = {
  hostname: 'whatever.com',
  port: 443,
  path: '/todos',
  method: 'POST',
  (or)
  method: 'PUT',
  (or)
  method: 'DELETE',
  headers: {
    'Content-Type': 'application/json',
    'Content-Length': data.length
  }
}

const req = https.request(options, res => {
  console.log(`statusCode: ${res.statusCode}`)

  res.on('data', d => {
    process.stdout.write(d)
  })
})

req.on('error', error => {
  console.error(error)
})

req.write(data)
req.end()