Back-end common sense that should be understood as a front-end

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What is a server

• server, also known as backend, server
• The front end is the visible and operable part of the user, such as branches and leaves
• The server provides "support" and "nutrition" for the front end, such as tree roots

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what is the front end

• Narrow sense: web page
• Broad sense: various clients, such as App, PC client, etc.

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Responsibilities of the server

• Provide the data to be displayed on the front end
• Receive the data to be submitted by the front end
• Store data (software companies value data very much and collect all kinds of data)

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server-side representation

• The front-end ajax needs to call an interface, such as using the get request to obtain data, and the post request to submit data
• This interface is provided by the server

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Front-end and back-end interactive communication - HTTP protocol

• Hypertext Transfer ProtocolHyper Text Transfer Protocol
• Specifies how the client and server communicate
• It is the standard and cornerstone of data communication in the Internet world

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HTTP - Generic

• url: the address of the back-end interface, that is, the address of the front-end Ajax request
• method: request method, such as GET POST PUT DELETE etc.
• Status code: the status returned by the interface, such as 200 302 404 500, etc.

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HTTP - Request

• Request: request, the front end sends to the server

• • Request Body: The request is the data sent to the backend
  • Request Content-type: the format of sending data, such as JSON format
  • ...

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HTTP - Response

• Response: return/response, the server returns to the front end

• • Response Body: the data returned from the backend to the frontend
  • Response Content-type: the format of the returned data, such as JSON format

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Demonstrate a Get request

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Demonstrate a POST request

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A web page may correspond to multiple servers

The resources that a web page needs to load may have

• html
• css
• js
• picture
• audio and video
• business data

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Different resources may come from different domain names

• html may come from a separate domain name
• js css may come from a separate domain name
• Data may come from a separate domain name
• Different domain names can correspond to different servers

The server can also be divided into static services (processing html css js images, etc.) and data services (providing data interfaces)

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How the server processes and returns data

• Define url rules for front-end requests - routing (url is required for front-end Ajax requests)
• Request to get data, use Response to return data

• • Also referred to simply as req and res
  • Obtainable through Request: method url body
  • Via Response: Can be set: status code, Content-type, body

• Read and store data - database

• • Database, dedicated to data storage and query
  • The database is an independent system, not exclusive to nodejs
  • Basic operations: query, add, delete, modify, sort, etc. all require query conditions

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What is a router

• Server-side entry rules
• Need to agree with the front end
• Just like the ancient city gates, the city gates have specific entrances to enter, and each entrance has a specific function
• Backend defines GET /api/list route => frontend axios.get( /api/list' ）
• Backend definition POST /api/create route => frontend axios.post( '/api/creaate' , {..)
• Routing defines the sending rules, and url is the specific sending form

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what does the route contain

• Define method, such as GET/POST, etc.
• Define url rules like /api/list and /api/create
• Define input (Request body) and output (Response body) formats

Configure the Nodejs environment

Enter Node official website to install:

After the installation is complete, use the following command to check whether the installation is complete:

• node -v
• npm -v

Continue to install the nrm management package source:

• npm i nrm -g
• nrm ls
• nrm use taobao

Use nvm to manage multiple versions of nodejs

• Mac OS, usebrew install nvm
• windows, search in github nvm-windows, there is a download address

use nvm

• nvm listView all current node versions
• nvm install v16.10.0Install the specified version
• nvm use —delete-prefix 16.10.0Switch to the specified version

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The difference between Nodejs and Javascript

Javascript

• Use ECMAScript syntax specification, plus Web API (DOM operation, BOM operation, Ajax), all are indispensable

• Combining the two, you can complete any operation on the browser side

• ECMAScript defines syntax (variable definition, loop, judgment, function, prototype and prototype chain, scope and closure, asynchronous, etc.), writing javascript and nodejs must be followed

Nodejs

• Use ECMAScript syntax specification, plus nodejs API, both are indispensable
• Handle http, handle files, etc. For details, refer to: nodejs.cn/api-v16/
• Combining the two, you can complete any operation on the server side

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CommonJs

• In the Nodejs environment, the module system is supported by default, and the module system follows the CommonJS specification
• A js file in Nodejs is a module

// index.js
function add(a, b) {
  return a + b;
}

function minus(a, b) {
  return a - b;
}

// 导出单个
module.exports = add;
// 在别的文件引入
// const add = require("index.js");

// 导出多个
module.exports = {
  add,
  minus
};
// 在别的文件引入
// const { add, minus } = require("index.js");

// 直接引入npm包
// const _ = require("lodash");

debugging

1. Use the breakpoint debugging that comes with vscode
2. Package.json --inspect=9229starts the program after adding parameters, enter the URL: chrome://inspect, and select the corresponding program debugger

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The difference between backend development and frontend development

service stability

• The server side may be subject to various malicious attacks and misoperations

• A single client can hang up unexpectedly, but the server cannot

Consider CPU and memory (optimization, scaling)

• The client monopolizes a browser, memory and CPU are not a problem
• The server side has to carry a lot of requests, CPU and memory are scarce resources

logging

• The front end will also participate in writing logs, but it is only the initiator of the logs and does not care about the follow-up
• The server side needs to record logs, store logs, and analyze logs, and the front end does not care

Safety

• The server side must be ready to receive various malicious attacks at any time, and the front end is much less
• Such as: unauthorized operation, database attack, etc.

Cluster and service split

• Product development is fast and traffic can increase rapidly
• How to carry large traffic by scaling machines and splitting services?

1. Front-end interview question bank ( necessary for interview) recommendation: ★★★★★            

Address: front-end interview question bank