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Node.js

Static website and Dynamic website

Static Website Dynamic Website
Content of Web pages can not be change at runtime. Content of Web pages can be changed.
No interaction with database possible. Interaction with database is possible
It is faster to load as compared to dynamic website. It is slower than static website.
Cheaper Development costs. More Development costs.
No feature of Content Management. Feature of Content Management System.
HTML, CSS, Javascript is used for developing the website. Server side languages such as PHP, Node.js are used.
Same content is delivered every time the page is loaded. Content may change every time the page is loaded.

網頁後端開發有很多語言

  • PHP
  • Node.js + Express + MongoDB
  • Java
  • Ruby on Rails
  • Python (Django)
  • .NET
  • ...

1. What is Nodejs ?

  • Node.js allows us to run JavaScript outside the browser (Therefore, it’s not only a programming language for front-end development.)

2. What is a Nodejs module ?

  • Module in Node.js is a simple or complex functionality organized in single or multiple JavaScript files which can be reused throughout the Node.js application.
  • There are built-in modules in Node.js, but we can also make our own modules or use modules from other people.

3. Module Wrapper

3.1 Difference of running codes in Node.js and Browser

  • The Module Wrapper
  • If we run JS code with Node.js, we can use modules and special Node.js syntax

3.2 What is Module Wrapper

  • 參考文件: Nodejs v16 Module Wrapper Docs
  • Before a module's code is executed, Node.js will wrap it with a function wrapper that looks like the following: 
    (function (exports, require, module, __filename, __dirname) {
  // Module code actually lives in here
});
  • It keeps top-level variables (defined with var, const or let) scoped to the module rather than the global object.
  • It helps to provide some global-looking variables that are actually specific to the module, such as:
    • The module and exports objects that the implementor can use to export values from the module.
    • The convenience variables __filename and __dirname, containing the module's absolute filename and directory path.

3. Self made module

3.1 一次導入一個

製作一個 .js 檔案，並設定其 exports

function morning(myName) {
  console.log("Good Morning " + myName);
}

exports.morning = morning;

用 require 導入

let try1 = require("./try1");

try1.morning("rjun");

3.2 一次導入多個

創建一個 directory 並把要導入 app.js 的 .js 檔案都丟進去， 並且在裡面創建一個 index.js 將要用的 module 都導入到裡面

Index.js

let try1 = require("./try1");
let try2 = require("./try2");

exports.morning = try1.morning;
exports.sayHi = try2.sayHi;

app.js

let greeting = require("./greeting"); // 會自動讀取到 index.js

greeting.morning("rjun");
greeting.sayHi("rjun");

4. Common Node Built-in Module

4.1 Path

The path module provides utilities for working with file and directory paths. It can be accessed using:

const path = require("path");
Syntax Description
path.basename(path[, ext]) returns the last portion of a path
path.extname(path) returns the extension of the path, from the last occurrence of the
 . (period) character to end of string in the last portion of the path.
path.join([...paths]) joins all given path segments together using the platform-specific separator
as a delimiter, then normalizes the resulting path.

4.2 URL

4.3 File System

writeFile

import { writeFile } from "fs";

writeFile("message.txt", "Hello Node.js", "utf8", callback);

readFile

import { readFile } from "fs";

// macOS, Linux, and Windows
readFile("<directory>", (err, data) => {
  // => [Error: EISDIR: illegal operation on a directory, read <directory>]
});

5. IP, DNS and Port

5.1 IP

  • IPv4 : 過去，IP 由 4 個 bytes 組成 ⇒ 32 bits ⇒ 2 ^ 32 ⇒ 42 億 9000 萬。不夠用！
  • IPv6 : 現在，IP 由 16 個 bytes 組成 ⇒ 128 bits ⇒ 2 ^ 128

5.2 DNS (Domain Name System)

  • DNS 伺服器將名稱請求轉換為 IP 地址
  • 例如將 www.example.com 這種人們可讀取的名稱轉換為 192.0.2.1 等數字 IP 地址
  • 網際網路 DNS 系統的工作原理和電話簿類似，管理名稱和數字之間的映射關係

5.3 Port

這裡指邏輯意義上的 Port，一般是指 TCP/IP 協議中的 Port，Port 號的範圍從 0 到 65535，比如用於流覽網頁服務的 HTTP 預設使用 80 Port，用於 FTP 服務的 21 Port 等等

6. Node Server

架一個本地伺服器(localhost)，監聽 3051 這個 port

// 取得 http module
const http = require("http")

// 建 server
const server = http.createServer((req, res) => {
	...
  res.write("Hello")
  res.end()
})

// 設定 port number
server.listen(3051, () => {
  console.log("Server is running on port 3501.")
})

但通常不會這樣寫，大多數人會使用 Express 框架來寫 node server

7. npm

  • Stands for node package manager.
  • It keeps tracks of what modules you get from outside.
  • Npm was installed with Node.js
  • 可以到 npmjs.com 找到別人做的 modules
  • 每次要用別人的 modules 都要用 terminal 到當前位址輸入 npm init 做好設定

npm module - nodemon

link → npm nodemon

好用的 module，當 js 檔案更新在 terminal 會自動更新