NodeJS

Quick Start

Basic Command

$ npm install express --save
$ npm install body-parser --save
$ npm install cookie-parser --save
$ npm install multer --save

How simple Node.js is ?

var express = require('express');
var app = express();
var fs = require("fs");

app.get('/listUsers', function (req, res) {
   fs.readFile( __dirname + "/" + "users.json", 'utf8', function (err, data) {
       console.log( data );
       res.end( data );
   });
})

var server = app.listen(8081, function () {

  var host = server.address().address
  var port = server.address().port

  console.log("Example app listening at http://%s:%s", host, port)

})

Version Checking

node -v
npm -version

nvm (node version manager) is a CLI to install different version of NodeJS

npm (node package manager) is a CLI for managing the node modues

Callback, Promise and Observable

callback - callbacks youtell the executing function what to do when the asynchronous task completes
promise - with promises the executing function returns a special object to you (the promise) and then you tell the promise what to do when the asynchronous task completes
observable - it's data stream…

promise

const promise = asyncFunc(function(resolve, reject) {.... });

promise.then(result => {
    console.log(result);
});

observable

const hello = Observable.create(function(observer) {
  observer.next('Hello');
  observer.next('World');
});

const subscribe = hello.subscribe(val => console.log(val));

From promise to observable, convert promise to observable

let Observable = Rx.Observable
let resultA, resultB, resultC

function addAsync (num1, num2) {
  const promise = fetch(`http://example.com?num1=${num1}&num2=${num2}`)
    .then(x => x.json())
  return Observable.fromPromise(promise)
}

addAsync(1, 2)
  .do(x => resultA = x)
  .flatMap(x => addAsync(x, 3))
  .do(x => resultB = x)
  .flatMap(x => addAsync(x, 4))
  .do(x => resultC = x)
  .subscribe(x => {
    console.log('total', x)
    conosle.log(resultA, resultB, resultC)
  })

compile ES6 to js

babel-node

https://medium.com/10coding/node-js-%E4%BD%BF%E7%94%A8-babel-%E5%81%9A-es6-%E9%96%8B%E7%99%BC-44b5b9e5f508

import and export

https://wohugb.gitbooks.io/ecmascript-6/docs/class.html

import {xxx, yyy} from './abc'

in abc file, export class xxx
export function yyy

import * as abc from './abc'
abc.xxx
abc.yyy()

import {xxx as a} from './abc'