Koa2 usingasyncandawaitTo handle asynchrony, the use function of the KOA2 instance takes middleware arguments.
Let’s start with a small core demo of KOA2
// Middleware repository
const arr = [
async (next) => {
console.log(1);
await next();
console.log(2);
},
async (next) => {
console.log(3);
await new Promise((resolve, reject) = > {
setTimeout(() = > {
resolve(
console.log(4)); },1000);
}); // The asynchronous operation await the following promise resolve before proceeding
await next();
console.log(5);
},
async (next) => {
console.log(6);
},
async (next) => {
// Will not be executed because next was not executed in the previous function
console.log(7);
await next();
console.log(8);
},
async (next) => {
// Will not be executed because next was not executed in the previous function
console.log(9); }];function fun(arr) {
function dispose(index) {
const currentFun = arr[index];
const next = dispose.bind(null, index + 1);
return currentFun(next); / / tail recursion
}
dispose(0);
}
fun(arr); // Prints 1, 3, 1 second and 4, 6, 5, 2
Copy the codeStart code (create a new ware.js file)
const http = require('http');
const urlParser = require("url"); // Parse the URL string and the URL object
class Middleware {
constructor() {
this.wares = []; // Storage middleware
};
use(fun) {
this.wares.push(fun); // Collect middleware
return this;
};
/* The core of middleware processing */
handleMiddleware(wareList) {
return function (ctx) {
// Middleware call
function dispose(index) {
const currentFun = wareList[index];
try {
// Wrap currentFun with promise.resolve to prevent currentFun from being passed in as a normal function
return Promise.resolve(
/* Dispose. Bind (null, index + 1) will not fetch the next middleware */
currentFun(ctx, dispose.bind(null, index + 1))); }catch (e) {
return Promise.reject(e); }}// Execute the first middleware of the repository immediately
dispose(0); }};createContext(req, res) {
const {method, url} = req;
const {query} = urlParser.parse(url, true);
/ /... It's a lot more complicated than that, so we're just going to do a simple package
return {
method, url, query,
res
};
}
serverHandle() {
return (req, res) = > {
// We trigger the middleware when the request comes in
const fn = this.handleMiddleware(this.wares);
// Get the context object for the current request
const ctx = this.createContext(req, res); fn(ctx); }};listen(. args) {
const app = http.createServer(this.serverHandle()); // This is just to simulate getting an HTTP serviceapp.listen(... args);// Directly to Node's native HTTP module
};
}
module.exports = Middleware;
Copy the codeTest (create a new demo.js file in the same directory)
const Demo = require("./ware");
const app = new Demo();
app.use(async (ctx, next) => {
await next();
console.log(`${ctx.method} ${ctx.url}`);
});
app.use(async ctx => {
ctx.res.end("hello world")}); app.listen(5000.() = > {
console.log("http://localhost:5000");
});
Copy the code