About using NPM

First of all, what is NPM?

——Node Package Manager. It is a package management tool for js.

Without further ado, download it first. (npm is released together with Node.js. As long as Node.js is installed, npm will also be installed)
After the installation is complete, the first thing to do is of course to test whether the installation is successful. Press win + R to open the cmd command prompt and enter npm -v. A prompt appears that the version was successfully installed.

npm -v3.10.10

If you installed an old version of npm, you can easily upgrade it through the npm command.
npm install npm@latest -g

Use the npm command to install the module

First create a new project folder on your computer and find the folder on cmd
C:\Users\filbert\Desktop> cd app2
C:\Users\filbert\Desktop\app2>

Initialize npm, npm init –yes

C:\Users\filbert\Desktop\app2>npm init --yes
Wrote to C:\Users\filbert\Desktop\app2\package.json:
{  "name": "app2",  "version": "1.0.0",  "description": "",  "main": "app2.js",  "scripts": {    
"test": "echo \"Error: no test specified\" && exit 1"
  },  "keywords": [],  "author": "",  "license": "ISC"}

Install the express framework, npm install express

C:\Users\filbert\Desktop\ch3>npm install express –save  
  npm WARN ch3@1.0.0 No description  
  npm WARN ch3@1.0.0 No repository field. 
   + express@4.15.4 updated
1 package in 3.63s

To build a node server in the project, you must first create a new js file, such as app2.js

const path = require('path');const express = require('express');
const app = new express();const port = 4000;//app.use(express.static('public'));
app.get('/*', (req, res) => {
    /*const pathname = req.params['0'];    if(!pathname) {
        res.sendFile(path.join(__dirname, 'index.html'));        return;
    }*/
    res.sendFile(path.join(__dirname+'/index.html'));
});var server = app.listen(port, (error) => {  if (error) {    console.error(error);
  } else {    console.info('==> Listening on port %s. Open up http://localhost:%s/ in your browser.', port, port);
  }
});

When you want to execute the server built by node.js, enter node app2.js## in cmd #

C:\Users\filbert\Desktop\app2>node app2.js
==> Listening on port 4000. Open up http://localhost:4000/ in your browser.

Copy http://localhost:4000/ to view the page

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