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Koa frame

2022-06-25 12:54:00 【BloggerM】

Koa frame

know Koa

We have learned before express, Another very popular Node Web The server framework is Koa.
Koa Official introduction ：
- koa：next generation web framework for node.js;
- koa：node.js The next generation of web frame ;
in fact ,koa yes express A new one developed by the same team Web frame ：
- At present, the core developers of the team TJ Our main energy is also in maintenance Koa,express It has been handed over to the team for maintenance ;
- Koa For the purpose of Web Applications and API Provide smaller 、 Richer and stronger capabilities ;
- be relative to express It has stronger asynchronous processing ability （ We will compare it later ）;
- Koa The core code of is 1600+ That's ok , Is a more lightweight framework , We can install and use middleware as needed ;
Actually, I learned express after , Study koa The process is very simple ;

Koa First experience

Let's experience koa Of Web The server

Create a new folder on the desktop learn_koa
Open the terminal initialization project npm init -y

stay package.json The configuration script

{
        
  "name": "learn_koa",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
        
    "start": "nodemon ./src/app.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
        
    "koa": "^2.13.4",
    "nodemon": "^2.0.16"
  }
}

Create a new file according to the script src, In the file src Next, create a new folder app.js
install koa frame npm i koa
Start project npm start

koa The registered middleware provides two parameters ：

ctx： Context （Context） object ;

koa Did not like express equally , take req and res Separate , But as ctx Properties of ;
ctx Represents the context objects requested in turn ;
ctx.request： Get request object ;

ctx.response： Get the response object ;

const Koa = require("koa");

const app = new Koa();

// context  Context object 
//  Contains two main objects  request responst
app.use((context, next) => {
        
  console.log(context);
  console.log(" Common middleware ");
});

app.listen(8888, () => {
        
  console.log(" The server is turned on successfully ");
});

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next： It's essentially a dispatch, Similar to the previous next;

Koa middleware

koa By creating app object , Registered middleware can only be registered through use Method ：
- Koa It didn't provide methods To register middleware ;
- There is no provision for path Middleware to match the path ;
But in real development, how do we compare the path and method Separation ？
- Mode one ： according to request Judge for yourself ;
- Mode two ： Use third-party routing middleware ;

Use of routes

koa The official does not provide us with a routing library , We can choose a third-party library ：koa-router
- npm install koa-router

We can encapsulate a user.router.js The file of ：

// router/user.js 
const Router = require("koa-router");

const userRouter = new Router({
      
  prefix: "/user",
});

userRouter.get("/", (ctx) => {
      
  //  In response to the results 
  ctx.body = " User list ";
});

userRouter.post("/", (ctx) => {
      
  //  In response to the results 
  ctx.body = " Add success ";
});
userRouter.delete("/", (ctx) => {
      
  //  In response to the results 
  ctx.body = " Delete successful ";
});
userRouter.patch("/", (ctx) => {
      
  //  In response to the results 
  ctx.body = " Modification successful ";
});

module.exports.userRouter = userRouter;

stay app Lieutenant general router.routes() Register as middleware ：

const Koa = require("koa");

const {
       userRouter } = require("./router/user");

const app = new Koa();

//  Register routing middleware 
// userRouter.routes()  Load routing rules 
// userRouter.allowedMethods()  Respond correctly to requests that are not implemented or used 
app.use(userRouter.routes()).use(userRouter.allowedMethods());

app.listen(8888, () => {
      
  console.log(" The server is turned on successfully ");
});

Be careful ：allowedMethods Used to judge a certain method Do you support ：
- If we ask get, Then it's a normal request , Because we have realized get;
- If we ask put、delete、patch, Then an error will be reported automatically ：Method Not Allowed, Status code ：405;
- If we ask link、copy、lock, Then an error will be reported automatically ：Not Implemented, Status code ：501;

Argument parsing ：params - query

Request address ：localhost:8888/user/2

obtain params：

// router/user.js

const Router = require("koa-router");

const userRouter = new Router({
        
  prefix: "/user",
});

userRouter.get("/:id", (ctx) => {
        
  // params  Mode reference 
  console.log(ctx.params.id);
  //  In response to the results 
  ctx.body = " User list ";
});

module.exports.userRouter = userRouter;

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Request address ：localhost:8888/user?name= Zhang San &age=21

obtain query：

// router/user.js

const Router = require("koa-router");

const userRouter = new Router({
        
  prefix: "/user",
});

userRouter.get("/", (ctx) => {
        
  // query  Mode reference 
  console.log(ctx.query);
  //  In response to the results 
  ctx.body = " User list ";
});

module.exports.userRouter = userRouter;

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Argument parsing ：json

Request address ：http://localhost:8888/user
- body yes json Format
obtain json data ：
Installation dependency ：npm install koa-bodyparser;

Use koa-bodyparser Middleware ;

At the entrance file index.js in

const Koa = require("koa");

const bodyParser = require("koa-bodyparser");

const {
         userRouter } = require("./router/user");

const app = new Koa();

// bodyParser()  analysis  json  Data middleware 
app.use(bodyParser());

//  Register routing middleware 
// userRouter.routes()  Load routing rules 
// userRouter.allowedMethods()  Respond correctly to requests that are not implemented or used 
app.use(userRouter.routes()).use(userRouter.allowedMethods());

app.listen(8888, () => {
        
  console.log(" The server is turned on successfully ");
});

stay router Below the file user.js in

// router/user.js

const Router = require("koa-router");

const userRouter = new Router({
        
  prefix: "/user",
});

userRouter.post("/", (ctx) => {
        
  // json  Mode reference 
  console.log(ctx.request.body);
  //  In response to the results 
  ctx.body = " Add success ";
});

module.exports.userRouter = userRouter;

Argument parsing ：x-www-form-urlencoded

Request address ：http://localhost:8888/user
- body yes x-www-form-urlencoded Format ：

obtain json data ：( and json It's consistent )

Installation dependency ： npm install koa-bodyparser;

Use koa-bodyparser Middleware ;

At the entrance file index.js in

const Koa = require("koa");

const bodyParser = require("koa-bodyparser");

const {
           userRouter } = require("./router/user");

const app = new Koa();

// bodyParser()  analysis  json  Data middleware 
app.use(bodyParser());

//  Register routing middleware 
// userRouter.routes()  Load routing rules 
// userRouter.allowedMethods()  Respond correctly to requests that are not implemented or used 
app.use(userRouter.routes()).use(userRouter.allowedMethods());

app.listen(8888, () => {
          
  console.log(" The server is turned on successfully ");
});

stay router Below the file user.js in

// router/user.js

const Router = require("koa-router");

const userRouter = new Router({
          
  prefix: "/user",
});

userRouter.put("/", (ctx) => {
          
  // json  Mode reference 
  console.log(ctx.request.body);
  //  In response to the results 
  ctx.body = " Modification successful ";
});

module.exports.userRouter = userRouter;

Argument parsing ：form-data

Request address ：http://localhost:8888/user/upload
- body yes form-data Format

analysis body Data in , We need to use multer

Installation dependency ：npm install koa-multer;

Use multer middleware ;

// router/user.js

const Router = require("koa-router");
const multer = require("koa-multer");
//  Pay attention to what I have installed here nanoid yes 3.x Version of , Other versions may report errors 
const {
         nanoid } = require("nanoid");
const {
         extname } = require("path");

const userRouter = new Router({
        
  prefix: "/user",
});

const storage = multer.diskStorage({
        
  destination(req, file, cb) {
        
    cb(null, "uploads/");
  },
  filename(req, file, cb) {
        
    //  file name 
    const fileName = nanoid();
    //  The suffix of the file 
    const extName = extname(file.originalname);
    cb(null, fileName + extName);
  },
});
//  Upload files 
const upload = multer({
        
  storage,
});
userRouter.post("/upload", upload.single("file"), (ctx) => {
        
  // form-data  Mode reference 
  //  file information 
  console.log(ctx.req.file);
  //  The form data 
  console.log(ctx.req.body);
  //  In response to the results 
  ctx.body = " File upload succeeded ";
});

module.exports.userRouter = userRouter;

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Data response

Output results ：body Set the response body to one of the following ：
- string ： String data
```
ctx.response.body = "hello world";
```
- Buffer ：Buffer data
- Stream ： Stream data
- Object|| Array： Object or array
```
// Object 
ctx.body = {
        
  name: "why",
  age: 18,
  height: 1.88,
};
```
```
// Array
ctx.body = ["abc", "def", "nba"];
```
- null ： Don't output anything
- If response.status Not set yet ,Koa Will automatically set the status to 200 or 204.

Request status ：status

ctx.status = 201;
ctx.response.status = 204;

Static servers

koa There is no built-in deployment related functionality , So we need to use a third-party library ：
- npm install koa-static

The deployment process is similar to express：

const Koa = require("koa");

const bodyParser = require("koa-bodyparser");
const static = require("koa-static");

const {
       userRouter } = require("./router/user");

const app = new Koa();

// bodyParser()  analysis  json  Data middleware 
app.use(bodyParser());

app.use(static("./dist/index.html"));

//  Register routing middleware 
// userRouter.routes()  Load routing rules 
// userRouter.allowedMethods()  Respond correctly to requests that are not implemented or used 
app.use(userRouter.routes()).use(userRouter.allowedMethods());

app.listen(8888, () => {
      
  console.log(" The server is turned on successfully ");
});

and express contrast

After learning the two frameworks , We should have found koa and express The difference between ：
In terms of Architecture Design ：
- express Is complete and powerful , It helps us build in many easy-to-use functions ;
- koa Is simple and free , It only contains the most core functions , There will be no restrictions on our use of other middleware .
  - Even in app Zhonglian's most basic get、post Didn't provide us with ;
  - We need to judge the request mode or other functions by ourselves or the origin ;
because express and koa The core of the framework is middleware ：
- But their middleware actually , The execution mechanism of their middleware is different , Especially when asynchronous operations are included in a middleware ;