Web developing

基本概念

MVC：为了解决直接用脚本语言嵌入HTML导致的可维护性差的问题，Web应用也引入了Model-View-Controller的模式，来简化Web开发。ASP发展为ASP.Net，JSP和PHP也有一大堆MVC框架。

目前，Web开发技术仍在快速发展中，异步开发、新的MVVM前端技术层出不穷。

由于Node.js把JavaScript引入了服务器端，因此，原来必须使用PHP/Java/C#/Python/Ruby等其他语言来开发服务器端程序，现在可以使用Node.js开发了！

Node.js开发优势

一是后端语言也是JavaScript，以前掌握了前端JavaScript的开发人员，现在可以同时编写后端代码；

二是前后端统一使用JavaScript，就没有切换语言的障碍了；

三是速度快，非常快！这得益于Node.js天生是异步的。

nodejs

特点

借助JavaScript天生的事件驱动机制加V8高性能引擎，使编写高性能Web服务轻而易举。

安装

https://nodejs.org/en/

NVM

Linux

Node Version Manager

curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.34.0/install.sh | bash

OSX

curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.34.0/install.sh | bash

append them into ~/.bash_profile

export NVM_DIR="$HOME/.nvm"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"  # This loads nvm
[ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"  # This loads nvm bash_completion

npm

Node Package Management

but doesn't make life easy executing any

curl -L https://www.npmjs.com/install.sh | sh

NPM by itself does not simply run any package. it doesn't run any package in a matter of fact. If you want to run a package using NPM, you must specify that package in your package.json file.

When executables are installed via NPM packages, NPM links to them:

1. local installs have "links" created at ./node_modules/.bin/ directory.
2. global installs have "links" created from the global bin/ directory (e.g. /usr/local/bin) on Linux or at %AppData%/npm on Windows.

npx

A tool for executing Node packages

npx will check whether <command> exists in $PATH, or in the local project binaries, and execute it.

if you wish to execute the locally-installed package some-package all you need to do is type:

npx some-package

Another major advantage of npx is the ability to execute a package which wasn't previously installed:

$ npx create-react-app my-app

The above example will generate a react app boilerplate within the path the command had run in, and ensures that you always use the latest version of a generator or build tool without having to upgrade each time you’re about to use it.

npm VS cnpm

npm其实是Node.js的包管理工具（package manager）

因为npm安装插件是从国外服务器下载，受网络影响大，可能出现异常，如果npm的服务器在中国就好了，所以我们乐于分享的淘宝团队干了cnpm这事。

proxy 配置

npm config set proxy http://127.0.01:8123
npm config set https-proxy http://127.0.0.1:8123

cnpm 使用

$ npm install -g cnpm --registry=https://registry.npm.taobao.org

hello world

'use strict';
console.log('Hello, World!');

全局对象

JavaScript有且仅有一个全局对象，在浏览器中，叫window对象。而在Node.js环境中，也有唯一的全局对象，叫global，

进入Node.js交互环境，可以直接输入：

> global.console
Console {
  log: [Function: bound ],
  info: [Function: bound ],
  warn: [Function: bound ],
  error: [Function: bound ],
  dir: [Function: bound ],
  time: [Function: bound ],
  timeEnd: [Function: bound ],
  trace: [Function: bound trace],
  assert: [Function: bound ],
  Console: [Function: Console] }

process 对象

process也是Node.js提供的一个对象，它代表当前Node.js进程。通过process对象可以拿到许多有用信息：

> process === global.process;
true
> process.version;
'v5.2.0'
> process.platform;
'darwin'
> process.arch;
'x64'
> process.cwd(); //返回当前工作目录
'/Users/michael'
> process.chdir('/private/tmp'); // 切换当前工作目录
undefined
> process.cwd();
'/private/tmp'

process 响应

在下一次事件响应中执行代码，可以调用process.nextTick()：

// test.js

// process.nextTick()将在下一轮事件循环中调用:
process.nextTick(function () {
    console.log('nextTick callback!');
});
console.log('nextTick was set!');

用Node执行上面的代码node test.js，你会看到，打印输出是：

nextTick was set!
nextTick callback!

这说明传入process.nextTick()的函数不是立刻执行，而是要等到下一次事件循环。

Node.js进程本身的事件就由process对象来处理。如果我们响应exit事件，就可以在程序即将退出时执行某个回调函数：

// 程序即将退出时的回调函数:
process.on('exit', function (code) {
    console.log('about to exit with code: ' + code);
});

全局strict 模式

省去每个js文件都加上'use strict';

node --use_strict example.js

判断JavaScript执行环境

有很多JavaScript代码既能在浏览器中执行，也能在Node环境执行，但有些时候，程序本身需要判断自己到底是在什么环境下执行的，常用的方式就是根据浏览器和Node环境提供的全局变量名称来判断：

if (typeof(window) === 'undefined') {
    console.log('node.js');
} else {
    console.log('browser');
}