Node.js基础汇总（一）：什么是Node.js，创建最简单的Node.js应用，NPM介绍，安装express模块

目录

1. 什么是Node.js？

1.1 JavaScript是什么？

1.2 Node.js 是什么？

1.3 Node.js的原理

2. 创建最简单的Node.js应用 

2.1 代码示例

2.2 分析Node.js 的 HTTP 服务器

2.3 运行结果

3. NPM介绍

3.1 什么是NPM

3.2 安装NPM

3.3 使用NPM命令安装模块，比如express模块

3.4 package-lock.json文件的说明

3.5 npm 的包安装分为：本地安装（local）、全局安装（global）

3.6 卸载模块

3.7 更新模块

3.8 搜索模块

3.9 创建模块

3.10 NPM常用命令

---

1. 什么是Node.js？

1.1 JavaScript是什么？

JavaScript是一门“完整”的语言。

它可以使用在不同的上下文中，其能力与其他同类语言相比有过之而无不及。

最早是运行在浏览器中，然而浏览器只是提供了一个上下文。

1.2 Node.js 是什么？

Node.js 就是运行在服务端的JavaScript。

Node.js事实上就是另外一种上下文，它允许在后端（脱离浏览器环境）运行JavaScript代码。

Node.js是一个基于Chrome JavaScript 运行时建立的一个平台。

Node.js是一个事件驱动I/O服务端JavaScript环境。

Node.js事实上既是一个运行时环境，同时又是一个库。

伴随着Node.js的还有许多有用的模块，它们可以简化很多重复的劳作，比如向终端输出字符串。

1.3 Node.js的原理

要实现在后台运行JavaScript代码，代码需要先被解释然后正确的执行。

Node.js的原理是，它使用了Google的V8虚拟机 （Google的Chrome浏览器使用的JavaScript执行环境），基于Google的V8引擎，来解释和执行JavaScript代码。V8引擎执行JavaScript的速度非常快，性能非常好。

2. 创建最简单的Node.js应用 

2.1 代码示例

2.2 分析Node.js 的 HTTP 服务器

（1）第一行请求（require）Node.js 自带的 http 模块，并且把它赋值给 http 变量。

（2）调用 http 模块提供的函数： createServer ，这个函数会返回 一个对象，这个对象有一个叫做 listen 的方法，这个方法有一个数值参数， 指定这个 HTTP 服务器监听的端口号。

2.3 运行结果

根据服务器运行的IP和端口号，在浏览器端访问，页面内容如下：

3. NPM介绍

3.1 什么是NPM

NPM是随同NodeJS一起安装的包管理工具，能解决NodeJS代码部署上的很多问题。

常见的使用场景有以下几种：

（1）允许用户从NPM服务器下载别人编写的第三方包到本地使用。

（2）允许用户从NPM服务器下载并安装别人编写的命令行程序到本地使用。

（3）允许用户将自己编写的包或命令行程序上传到NPM服务器供别人使用。

3.2 安装NPM

由于新版的nodejs已经集成了npm，所以之前安装nodejs时，npm也一并安装好了。

通过输入命令 "npm -v" 来测试是否成功安装。

3.3 使用NPM命令安装模块，比如express模块

（1）语法： $ npm install

（2）示例：用npm安装express

安装好之后，express 包就放在了工程目录下的 node_modules 目录中，因此在代码中只需要通过 require('express') 的方式就好，无需指定第三方包路径。

用npm list express查看安装的express版本。

 

3.4 package-lock.json文件的说明

上述安装完模块后，在模块的目录下，会自动生成package-lock.json文件，该文件定义包的属性。

（1）package-lock.json 属性说明

• name - 包名。

• version - 包的版本号。

• description - 包的描述。

• homepage - 包的官网 url 。

• author - 包的作者姓名。

• contributors - 包的其他贡献者姓名。

• dependencies - 依赖包列表。如果依赖包没有安装，npm 会自动将依赖包安装在 node_module 目录下。

• repository - 包代码存放的地方的类型，可以是 git 或 svn，git 可在 Github 上。

• main - main 字段指定了程序的主入口文件，require('moduleName') 就会加载这个文件。这个字段的默认值是模块根目录下面的 index.js。

• keywords - 关键字

（2）文件完整内容：

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3.5 npm 的包安装分为：本地安装（local）、全局安装（global）

（1）两种安装方式的命令格式：

 如果报错：npm err! Error: connect ECONNREFUSED 127.0.0.1:8087

 解决办法：$ npm config set proxy null

（2）本地安装：

• 将安装包放在 ./node_modules 下（运行 npm 命令时所在的目录），如果没有 node_modules 目录，会在当前执行 npm 命令的目录下生成 node_modules 目录。
• 可以通过 require() 来引入本地安装的包。

（3）全局安装：

• 将安装包放在 /usr/local 下或者你 node 的安装目录。
• 可以直接在命令行里使用。

3.6 卸载模块

3.7 更新模块

3.8 搜索模块

3.9 创建模块

创建模块，package.json 文件是必不可少的。

我们可以使用 NPM 生成 package.json 文件，生成的文件包含了基本的结果。

3.10 NPM常用命令

（1）​​​​​NPM提供了很多命令，例如install和publish，使用npm help可查看所有命令。

（2）使用 npm help 可查看某条命令的详细帮助，例如npm help install。

（3）在package.json所在目录下使用 npm install . -g 可先在本地安装当前命令行程序，可用于发布前的本地测试。

（4）使用 npm update 可以把当前目录下node_modules子目录里边的对应模块更新至最新版本。

（5）使用 npm update -g 可以把全局安装的对应命令行程序更新至最新版。

（6）使用 npm cache clear可以清空NPM本地缓存，用于对付使用相同版本号发布新版本代码的人。

（7）使用 npm unpublish @可以撤销发布自己发布过的某个版本代码。