Koa2 fast build server

Get started

1. New folder initialization project , Command line input npm init -y
2. install koa, Input npm i koa
3. Create a new app.js file
   
4. app Content

   // 1.  establish KOA Instance object of 
   const Koa = require('koa')
   const app = new Koa()
   // 2.  Binding middleware ( Write response functions )
   // ctx:  Context ,web Containers ,ctx.request ctx.response
   // next:  Next middleware , Whether the next layer middleware can be implemented , Depending on next Is this function called 
   app.use(async (ctx,next) => {
         
   	//  What I just did in middleware 
      ctx.response.body = 'Hello world!'
      await next() // next() Back to a promise object 
      //  What to do after all the middleware in the inner layer 
   })
   ...
   // 3.  Monitor port number 
   app.listen(8888)
   

project

Get ready

1. Initialize project
2. install koa
3. establish middleware Folder ： Storage middleware （koa_response_data.js、koa_response_duration.js、koa_response_header.js）
4. establish data Folder ： For storage data data , Simulate getting data from a database
5. establish utils Folder ： Deposit file_utils.js, obtain data File data method
6. To write app.js file

   //  The server's entry file 
   // 1. establish KOA Instance object of 
   const Koa = require('koa')
   const app = new Koa()
   // 2. Binding middleware 
   //  The total time is 
   const respDurationMiddleware =  require('./middleware/koa_response_duration')
   app.use(respDurationMiddleware)
   //  Response header middleware 
   const respHeaderMiddleware = require('./middleware/koa_response_header')
   app.use(respHeaderMiddleware)
   //  Logic processing middleware 
   const respDataMiddleware = require('./middleware/koa_response_data')
   app.use(respDataMiddleware)
   // 3. Binding port number  8888
   app.listen(8888)
   

7. To write koa_response_duration.js file （ The total time is ）

   //  Middleware for computing server consumption 
   module.exports = async (ctx, next) => {
         
   //  Record the start time 
   const start = Date.now()
   //  Let the inner middleware be implemented 
   await next()
   //  Record the end time 
   const end = Date.now()
   //  Set the response header  X-Response-Time
   const duration = end - start
   // ctx.set  Set the response header 
   ctx.set('X-Response-Time', duration + 'ms')
   }
   

8. To write koa_response_header.js file （ Response header middleware ）

   //  Middleware for setting response headers 
   module.exports = async (ctx, next) => {
         
   const contentType = 'application/json; charset=utf-8'
   ctx.set('Content-Type', contentType)
   ctx.set("Access-Control-Allow-Origin", "*")
   ctx.set("Access-Control-Allow-Methods", "OPTIONS, GET, PUT, POST, DELETE")
   await next()
   }
   

9. To write koa_response_data.js file （ Logic processing middleware ）

   //  Middleware for business logic , Read something json File data 
   const path = require('path')
   const fileUtils = require('../utils/file_utils')
   module.exports = async (ctx, next) => {
         
   //  according to url
   const url = ctx.request.url // /api/seller ../data/seller.json
   let filePath = url.replace('/api', '') // /seller
   filePath = '../data' + filePath + '.json'  // ../data/seller.json
   filePath = path.join(__dirname, filePath)
   try {
         
   	const ret = await fileUtils.getFileJsonData(filePath)
   	ctx.response.body = ret
   } catch (error) {
         
   	const errorMsg = {
         
   	message: ' Failed to read file contents ,  File resource does not exist ',
   	status: 404
   	}
   	ctx.response.body = JSON.stringify(errorMsg)
   }
   
   console.log(filePath)
   await next()
   }
   

10. To write file_utils.js file

    //  Tools and methods for reading files 
    const fs = require('fs')
    module.exports.getFileJsonData = (filePath) => {
          
    //  According to the path of the file ,  Read the contents of the file 
    return new Promise((resolve, reject) => {
          
    	fs.readFile(filePath, 'utf-8', (error, data) => {
          
    	if(error) {
          
    		//  Failed to read file 
    		reject(error)
    	} else {
          
    		//  Read file successful 
    		resolve(data)
    	}
    	})
    })
    }