Koa learning

Koa-like understanding

Koa is a lightweight, robust and expressive nodejs framework created by the original express team.

Use Koa

• koa cheap
  * $ npm i koa
• A simple koa server

const Koa = require("koa");
//koa正常使用
let app = new Koa();
//使用  会有一个回调函数

ctx:   context对象
 app.use(async (ctx) => {
    
    
     //ctx.request === req;   ctx.response === res;
     // ctx.response.body = "hello world";

     ctx.body = "hello "
     console.log(ctx.url);
 })

• Koa uses middleware to control "upstream" and call "downstream";
• Koa is an object containing a set of middleware functions; the functions in app.use can be understood as middleware
• Transfer control to another middleware through next();

let m1 = async function(ctx, next) {
    
    
    console.log("m1");
    //ctx.state     传递数据
    //它就像一个中间间的贡献空间
    ctx.state = {
    
    
            perPage: 5,
            totalPage: "13"
        }
        //将控制权，交给下一个中间件
    next(); //  ----->m2

    // console.log("m1   end");
}
let m2 = async function(ctx, next) {
    
    
    // console.log("m2");
    console.log(ctx.state);
    ctx.state = {
    
    
        p: 1,
        id: 14,
        totalPage: 3
    }

    next(); //------->下一个中间件

    // console.log("m2   end");
}
let m3 = async function(ctx, next) {
    
    
    // console.log("m3");
    //     next();

    // console.log("m3   end");
    console.log(ctx.state);
    ctx.body = "hello";
    //状态码
    // ctx.status = 404
}

// 中间件在实际使用,全部都是模板
app.use(m1);
app.use(m2);
app.use(m3);

Koa commonly used middleware

Also router

installation

npm i koa-router -S

use

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

let app = new KOa();
let router = new Router();

router.get("/", async ctx => {
    
    
    //会将   /  和  /index的请求，返回同一页面
    ctx.redirect("/index");
    ctx.body = "hello world";
})

router.get("/datail", async ctx => {
    
    
    ctx.body = "详细页";
})

router.get("/getData", async ctx => {
    
    
    // let indexData = fs.readFile("index.html");

    let indexData = "w我是读取模板";
    //简写
    // ctx.body = {
    
    
    //     indexData
    // }

    ctx.render("/index2", {
    
    
        indexData
    })
})
app.use(router.routes());
app.listen(8889);

RESTful: Interface design principles
post/get
wrong approach
localhost:8000/adduser
localhost:8000/deleteuser
localhost:8000/uodateuser
localhost:8000/getuser

Correct approach
localhost:8000/user request method get get
localhost:8000/user delete delete
localhost:8000/user put update
localhost:8000/user post add

REST design generally meets the following conditions:
programs or applications should be abstracted as resources.
Each resource corresponds to a unique URI (uri is a uniform resource identifier).
Use a unified interface to operate
on the resource. Various operations on the resource will not change the resource. identifies
all operations are stateless

koa-views

• A dress koa-views

npm i koa-views -S

• use

const Views = require("koa-views");
app.use(Views(__dirname + "/views", {
    
    
    extension: "pug"
}));
router.get("/", async ctx => {
    
    
    // ctx.body = "hello world";
})
app.use(router.routes());

app.listen(8081);

koa-static

• koa-static is a middleware for loading static resources, through which static resources such as css and js are loaded;
• Anthropomorphic koa-static

npm i koa-static

Use koa-static

const static = require("koa-static);
app.use(static(__dirname+"/static))//加载静态文件的目录