NodeJS is introduced

What is NodeJS

• Node.js is a JavaScript Runtime built on Chrome’s V8
• Node.js uses an event-driveb, non-blocking I/O model

Non-blocking I/O

• Blocked: The process hibernates during I/O and waits for the I/O to complete
• Non-blocking: When I/O, the function returns immediately and the process does not wait for the I/O to complete

event-driven

• Notification after an asynchronous operation such as I/O is complete
• Observer model

Why NodeJs

• A larger range of front-end responsibilities and a unified development experience
• It has obvious advantages in processing high concurrency and I/O intensive scenarios

CPU intensive VS I/O intensive

• CPU intensive: CPU actions (compression, decompression, encryption, decryption) such as computation and logical judgment are spent most of the time.

• I/O intensive: most of the time is spent reading access devices, network facilities (file operations, network operations, databases)

  • Common Web Scenarios
    • Static resource reading
    • Database operations
    • To render the page

High concurrency solutions

• Increase number of machines
• Increased number of cpus per machine – multi-core (increased computing power)

Basic knowledge

• process

  • A program in a computer is a running activity on a data set. It is the basic unit of resource allocation and scheduling in a system

  • Multi-process: Start multiple processes that can perform multiple tasks together

  • A single CPU can run multiple processes at the same time

    • Similar to the principle of animation, to the human eye can not perceive the speed of the play between multiple tasks (process) back and forth

• thread

  • A relatively independent, schedulable unit of execution within a process that shares the resources of the process with threads belonging to the same process

  • Starting a process You can start multiple threads within a process, which can perform multiple tasks together

• I/O classification and detailed explanation

• NodeJs working model

  

  NodeJs working model

  • Only one process is enabled for a single thread, and only one thread is enabled for a process (i.e. only one process is enabled for a CPU, and only one thread is enabled for a process)
    • Single thread is only for the main process, the I/O operating system multithreading scheduling (asynchronous operations are part of the I/O operating system multithreading operations have nothing to do with NodeJS, NodeJS[the main process] initiates a request, sends the request to the I/O)
  • A single thread is not a single process.

• Common scenario

  • Web scenario: High concurrency and I/O intensive
  • web server
  • Native code building
  • Utility development

Debug project & initialization

The environment

• CommonJS (Module Specification)

  • Each file is a module and has its own scope (modules loaded are not loaded again, but directly take the result of the module loaded).
  • Inside the module, the Modeule variable represents the module itself
  • The module.exports property represents the module’s external interface

• Global (no BOM, DOM, window)

  • Similar to the window
  • Buffer(binary data processing), process.console
  • timer

• process

  • Process. NextTick micro tasks

    debugging

• Inspector

• VS Code

Based on the API

path

• _dirname, _filename always returns the absolute path to the file
• Process.cwd () always returns the folder where the node command was executed

. /

• Always relative to the current file folder in the require method
• As with **process.cwd()** elsewhere, start folders relative to Node

Buffer(directly mounted in global)

• Buffers are used to process binary data streams
• Instance is like integer array, fixed size (default hexadecimal, cannot change length)
• C++ code allocates physical memory outside the V8 heap

Simple Web Server

Using the Supervisor file to listen for changes Using the Handlebars template engine using the **curl simulation request Web server (MAC) Using Commander or yargs** to get the command line argument list

Implement a static resource server

Run the command to change the local directory into the root directory of a static resource server. You can access the file Anywhere through the URL

Basic steps

• To achieve the file read and write, and in the corresponding Host:port open
• Set up the NPM configuration and upload it to the NPM generate NPM CLI

.gitignore

• Before the matching mode, /: indicates the project root directory
• A /: at the end of a matching pattern indicates a directory
• Match pattern before add! : represents the inverse
• * : indicates any character
• ? : Matches any character
• **: matches multi-level directories

.npmignore

.npmignore details

EditorConfig

Set range for the file

• RequestHeader set
  • range: bytes=[start]-[end]
• ResponseHeader set
  • Accept-Range: bytes
  • Content-Range: bytes start-end/total

Cache headers

• responseHeader
  • Expirse (returns absolute time)
  • Cache-control (returns the relative time of the last request max-age)
• If-modified-since/last-modified
  • requestHeader: If-Modified-Since
  • responseHeader: Last-Modified
• If-none-match/ETag Request cache flow

The semantic version number is X.Y.Z

• Update Z bit: Bug fix
• Upgrade Y bit: new features and compatibility with previous and bug fixes
• Upgrade X bit: Compatibility is not guaranteed (generally even is stable version)
• x.y.*:
  • For example, 1.2.* : automatically updates z bits, and the latest bug fix is the same as ~1.2.0
  • X/y fixed
• X and ^2.0.0

In Linux, you need to assign operation rights to files

Local building

Super easy version to build

• The compression
• Less/SCSS is built as CSS, ES5/ES6 is built as browser-recognized version, etc

gulp

babel

webpack

Unit testing & Release

Assertions library

Mocha

Example NodeJS crawlers

Simple climb baidu picture

• A program that automatically captures network information according to certain rules (search engine)

  • Crawl to HTML
  • Cheerio converts HTML to a JQ-like object (you can use JQ operations to get information)

• The crawler

  • User-agent, Referer, verification code
  • Number of visits between units, number of visits
  • Key information picture confusion
  • Asynchronous loading