An in-depth analysis of the installation method and module system of Nodejs

This article will introduce to you the installation method of Nodejs and the module system of Nodejs.

About NodeJS

Node.js is a Javascript runtime environment based on the Chrome V8 engine. [Recommended learning: "nodejs Tutorial"]

• In our daily development, most Web projects use the front endJS is written, and the backend is written in server-side language, such as JAVA PHP GO, but because Node# The birth of ## allows front-end developers to use JS to write server code, so the birth of Node can be said to make the front-end shine, and both the front-end and the back-end blossom.
Especially
• Node provides the basis for the development environment to run. Front-end frameworks like Vue React that we usually use have become very Powerful, it can be said to be an essential basic device for the front end.
• Node There are more people using it, and more and more people are using JS on our front-end to contribute to open source. The npm library has become a A very large code warehouse. In the npm package management system, we can find the plug-ins and wheels we need. We can use them directly, which also saves us developers money. A lot of valuable time.
The introduction and function of more
• NodeJS has been introduced very clearly in this article. If you are interested, you can take a look at Portal.

NodeJS installation

• NodeJSWe can download it from his official website.

Choose the appropriate version for you to download. Since my computer has already installed it, I won’t demonstrate it anymore. Just open the installation program and go to the next step. Okay, if you want to see a more detailed installation guide and global configuration guide, you can see this article:
• Node.js Installation and Environment Configuration for Windows
After installation, we need to check If the installation is successful, you can open the terminal and enter
• node -v.

You can see that we have installed the latest version of
• node #16.6.1.

node
• , we can type node in the terminal to enter Interactive mode and enter a must-have code for our programmers hello world.

JS
• file for execution.

  echo test>helloWorld.js

  rrree

• 我们只需要键入node+文件名即可执行这个文件。

NodeJS模块

• Node应用由模块组成，采用的CommonJS模块规范。每一个文件就是一个模块，拥有自己独立的作用域，变量，以及函数等，对其他的模块都不可见，而文件路径就是模块名,所以我们需要了解不同模块之间是怎么交互怎么互相使用的。
• 模块可以多次加载，但是只会在第一次加载时运行一次，模块加载的顺序，按照其在代码中出现的顺序。
• 在编写每个模块时，都有require、exports、module三个预先定义好的变量可供使用。

加载(require)

• require意为需要的，也就是说我们可以通过require来引入我们需要的模块，

let x=require('./hello')
let y=require('./hello.js')

• 我们可以这样引入一个模块，require后面可以接收一个地址，可以是绝对路径也可以是相对路径。
• 值得注意的是，我们的后缀.js扩展名可以省略不写。

导出(exports)

• exports意为导出，也有一种说法是暴露，我们一般可以使用exports用于导出模块公有函数和属性。

/* hiNode.js */
exports.addIce=function(){
  console.log('我在加冰')
}

• 我们在hiNode.js文件中暴露了一个函数addIce，这样我们可以在别的地方require这个模块并使用该函数。

/* helloWorld.js */
let x=require('./hiNode')
x.addIce()

• 我们在终端键入node helloWorld.js。

• 成功引入了模块并使用函数。

模块对象(module)

• 在Node中我们通过module可以访问到当前模块的一些信息。

/* hiNode.js */
exports.addIce=function(){
  console.log('我在加冰')
}
console.log(module)

• 可以看到我们打印的module里面有它导出的函数，文件名，路径等信息。实际上当我们require一个模块的时候，它读取的就是该文件的module.exports变量。
• 这个module.exports变量一般是对象的形式如上图，所以我们经常最常用到module是为了改写module.exports变量这个导出变量，我们可以改成函数形式。

/* hiNode.js */
module.exports=function(){
  console.log('直接可以调用，我是一个函数')
}

/* helloWorld.js */
let x=require('./hiNode')
x()

• 如上我们直接可以使用x是因为require了一个函数，模块默认导出对象被替换为一个函数。

写在最后

总的来说NodeJS应用是由模块组成的，我们可以在js文件导出exports函数等变量，在另一个js文件进行导入require这个模块。

更多编程相关知识，请访问：编程入门！！

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