I. Global module

Definition: Access anytime, anywhere, no reference required.

Process. env returns information about the environment variable in which the project is running. Process. argv argument array (can receive arguments passed in when executing node by command), parameter 1: returns the current node path, parameter 2: returns the current file path

Example (index.js) :

let num1 = parseInt(process.argv[2]);
let num2 = parseInt(process.argv[3]);
console.log(num1 + num2);
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Enter the command:

node index 2 3
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Output:

5
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System module

Definition: Requires the require() reference, but does not require a download (it was built in when node was installed). Path: Utility for handling file paths and directory paths.

let path = require('path')
p = '/node/a/1.jpg'
path.dirname(p)   // Path (/node/a)
path.basename(p)  // File name (1.jpg)
path.extname(p)   // File extension (.jpg)
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Fs: used for file read and write operations.

let fs = require('fs')
fs.readFile('./a.text'.(err,data) = > {
   if(err) {
         console.log(err)
    } else {
        console.log(data.toString())
    }
 })
 // Add content to the file
 fs.writeFile('a.txt'.'test', { flag: 'a' }, (err) = > {
    if (err) {
        throw err
    }
})
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3. Custom modules

Definition: require encapsulates its own module.

1, the require

1) If there is a path, go to the path;

const mod1 = require('./mod')
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2) If not, go to node_modules;

const mod1 = require('mod')
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3) If none exists, go to the Node installation directory.

Exports and Modules

1) value

exports.a = 1;
exports.b = 2;
let c = 3;
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Use:

mod1.a    mod1.b
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2) object

module.exports = { a:1.b:2 }
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Use:

mod1.a    mod1.b
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3) function

module.exports = function() {}Copy the code

Use:

mod1()
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4) class

module.exports = class {
   constructor(name) { this.name = name }
   show() { console.log(this.name) }
}
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Use:

let p = new mod1('myname'); 
p.show()
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4. HTTP module (key)

The template string ‘(the key to the left of the number 1) to recognize ${}.

let http = require('http')
let fs = require('fs')

http.createServer((request, response) = > { // Create an HTTP service
    fs.readFile(`. /${request.url}`.(err, data) = > { // Read file (path, callback)
        if (err) {
            response.writeHead(404) //200 is the default
            response.end('404 not found')}else {
            response.end(data)
        }
    })
}).listen(8088)// To create a server, you must use a listening port
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