Beginner node (1)

1. What is Node?

Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine .

No need to deal with compatibility issues 2009.05

1.1Node is a JS operating environment

​ How js works:

1. Client: Import the js file, then open the browser and view it in the console

2.node server:

​ 1. In the cmd window, use the cd command to switch to the folder that needs to be opened, and run the node file name

2. Shift + right click directly under the folder

​ 3. The vscode editor is directly opened in the terminal of the current file, and the submint editor needs to install the terminal plug-in

1.2 Comparing JS in the browser

1.2.1 JS in the browser

​web api provides functions for manipulating browser windows and pages. For example: BOM manipulation, DOM manipulation, AJAX

​These features have limitations. For example: cross-domain issues, file reading and writing

1.2.2 JavaScript in Node

​nodeAPI provides almost everything that can be done

1.2.3 JS in Node vs. JS in the browser

​ ① The browser provides limited capabilities, and JS can only use the functions provided by the browser to do limited operations

② Node provides a complete ability to control the computer. NodeJS can almost control the entire operating system through the interface provided by Node.

1.3 Official documents

​ Node official website: https://nodejs.org/en/

​ Node Chinese official website (private website): http://nodejs.cn

2. What can Node do?

2.1 Developing desktop applications

​ For example, QQ, WeChat... VScode, which is often used, is developed with node

2.2 Developing server applications

Structure 1: Microstructure

​ The Node server needs to complete request processing, response, interaction with database, and various business logics

​ This structure is usually applied to micro sites. For example: personal blog, company official website

Structure 2: Large Structures

​ This structure is very common and is used on sites of all sizes

Node server

​ Do not do anything related to business logic. Most of the time, it is simply forwarding the request. but may have some extra features

​ 1. Simple information records: request logs, user preferences, advertising information

2. Static resource hosting

3. Cache

backend server

​ Handle large business logic

3. Why learn NodeJS?

1. JS development saves time and effort

2. Because nodeJS is single-threaded, there is no loss of thread switching and no competition between threads.

3. IO processing is very fast

4. Node is not suitable for complex operations, for example, java can open multiple threads for parallel operations

​ Node can do everything that other server-side languages ​​(such as java, .net) can do. Language is not good or bad, only suitable for the scene.

​ Node developers are looking for a fast IO processing language, so they choose JavaScript

4. Global object

global

​ Same as this in the browser environment, representing the top-level object

​ Note: the browser's global environment this means window, this in node does not mean global

// 全局对象
console.log(global)
console.log(this)//在node中的this不指向window，就是一个空对象

var a = 123;
console.log(global.a == a)//在node中变量声明不提升至global中
console.log(a)

1.setTimeout，setInterval

The usage is exactly the same as the browser environment.

​ Note: The browser returns the ID, and the object is returned in the node environment

2.setImmediate

​Similar to setTimeout 0

setInterval(()=>{
    console.log(123)
},1000)

setTimeout(() => {
    console.log("延时定时器")
},0);


setImmediate(()=>{
    console.log("qwe")
},0)

3.console

​ The browser outputs in the console

​ node output on the command line

4.__address*

console.log(__dirname)

​ Get the directory where the current module is located

​Note : not a global attribute

5.__filename*

console.log(__filename)

​ Get the file path of the current module

​Note : not a global attribute

6.Buffer

Buffer is similar to an array, it is a data transmission format, the difference between hexadecimal numbers and strings:
the string is read-only, and a new string can be obtained by modifying the string, and the original string remains in the original
buffer memory The allocation is not in the heap memory of v8, and the application of separate memory is realized at the c++ level in node.
Typed array

​ Inherited from UInt8Array

​ The basic unit of storage in a computer: byte

​ It may be necessary to use hexadecimal representation when using and outputting

7.process

cwd()

​ Return the working directory of the current nodejs process, the directory of the running cmd window

exit()*

​ Force quit the current node process

​ The exit code can be passed in, 0 means successful exit, the default is 0, mainly for input into the log

argv*

​ Get all parameters in the command

platform

​ Get the current platform system

kill(pid)

​ Kill the process according to the process ID

env

​ Get the environment variable object

5. Node modularization

1. Module search

1. Relative path

2.1 Add./ Situation

​ On the server side, be sure to add ./, which means starting from the current directory

2.2 Without ./case

​ ① Check whether it is a built-in module, such as: fs, path, etc.

② Check the node_modules in the current directory

③ Check the node_modules in the parent directory

3. Suffix name

​ If no suffix is ​​provided, auto-completion

​ The order of completion is: js, json, node, mjs

4. File name

​ If only a directory is provided and no file name is provided, index.js in this directory will be automatically searched

5. Run node ./

​ The main field in package.json, the default value is index.js

2. module object

​ Record the information of the current module

3. require function

​ The resolve function is spliced ​​into an absolute path

4. Modular principle

When executing a module or using require, the module is placed in a function environment

6. Basic built-in modules

(After downloading the number node, it will automatically package the module for you)

1.os

​ Reference address: https://nodejs.org/dist/latest-v12.x/docs/api/os.html

1.EOL

​ Operating system version

2.arch()

​ Operating system CPU architecture

3.cpus()

​ CPU core information

4.freemem()

​ How much memory is left in the computer, returned as bytes

5.homedir()

​ User directory

6.hostname()

​ hostname

7.tmpdir()

​ Get temporary file directory

2.path

​ Reference address: https://nodejs.org/dist/latest-v12.x/docs/api/path.html

​Note : The operations of the path module are all equivalent to string operations, and will not determine whether the path actually exists

1.basename

​ Get the last/behind content of a certain path

​ The second parameter is an optional parameter, if it matches, remove the matching content

2.sep

​ operating system delimiter

3.delimiter

​ Output the separator of the current operating system

4. dirname

​ Get the directory of the path

5.extname

​ Get the suffix of the path

6.join

​ The splicing path will be spliced ​​according to the operating system

7.normalize

​ According to the operating system specification path

8.relative

​ Change to a relative path format

9.resolve*

​ Convert to an absolute path, splicing according to the cmd window

​Note : Compared with command-line tools, it is generally used with __dirname

3.url

​ Reference address: https://nodejs.org/dist/latest-v12.x/docs/api/url.html

1.parse()*

​ convert string to object

2.format()

​ object converted to string

4.util

​ Reference address: https://nodejs.org/dist/latest-v12.x/docs/api/util.html

1.callbackify

​ Convert asynchronous function to callback form

2.promisify

​ The callback form is converted into an asynchronous function

3.isDeepStrictEqual

​ Depth comparison of two objects

7. Document I/O

1. I/O：input output

​ Input and output to external devices (disks, network cards, graphics cards, printers...)

​ The speed of IO is often lower than the interaction speed of memory and CPU

2. fs module

​ Reference address: https://nodejs.org/dist/latest-v12.x/docs/api/fs.html

1. fs.readFile

​ read a file

2. fs.writeFile

​ Write content to the file

​If the file

3.fs.stat

​ Get file or directory information

1.size

​ Occupied bytes

2.atime

​ Last Access Time

3.mtime

​ Last time the content of the file was modified

4.ctime

​ Last time the file status was modified

5.birthtime

​ File creation time

6.isDirectory()

​ Determine whether it is a directory

7.isFile()

​ Determine whether it is a file

4.fs.readdir

​ Get files and subdirectories in a directory

5.fs.mkdir

​ Create directory

6.fs.exists

​ Determine whether a file or directory exists

Eight. Front-end interview questions (1)

1. Implement setInterval with setTimeout

function mySetTimout(fn, delay) {
    let timer = null
    const interval = () => {
        fn()
        timer = setTimeout(interval, delay)
    }
    setTimeout(interval, delay)
  
}

// 测试
const { cancel } = mySetTimout(() => console.log(888), 1000)

2. Implement setTimeout with setInterval

function mySetInterval(fn, delay) {
            const timer = setInterval(() => {
                fn()
                // clearTimeout(timer)
                clearInterval(timer)
            }, delay)
        }

        // 测试
        mySetInterval(() => console.log(888), 1000)