I always feel that express's middleware system is a very image of streamlined processing, just like the processing pipeline, each link completes its own work for different parts of the same product, and finally gets a finished product. Today we will implement a simple middleware queue.

I. API level

• Initialization method

  let middleware = new MiddleWare();

• Method of Adding Middleware Functions

  // Fn is added middleware.use(Fn);

• Start middleware queues

  middleware.start(req, res);

2. Definition of Core Classes

class MiddleWare{    constructor(){        this.queue = [];//Used to store middleware queues
    }    //Add Middleware
    use(fn){         this.queue.push(fn);//Add custom middleware to the queue
    }    //Executing Middleware in sequence
    start(req, res){        let i = 0;//Execution pointer

        //Actuator
        const next = (err)=>{            //If there is an error, hang the error message on response and exit directly.
            if(err){
                res.hasError = true;
                res.data = err.toString();                return;
            }            //If there are no errors, check to see if it reaches the end of the queue, and if not, continue executing the next Middleware
            if(i < this.queue.length){                this.queue[i++](req, res, next);                /*Pass next directly into the currently executed function as a callback
                 At any stage of execution of the current execution function, the relevant information can be passed to the next middleware by calling the next method on its own initiative.*/
            }else{                //If it's at the end of the team, it's over.
                console.log('finish');
            }

        }        //Start the first
        next();
    }
}

3. Use the use method to add Middleware

//Add the first middleware/*
Here is a demonstration of a basic error capture approach when an error occurs in the middleware,Errors are caught and passed in next
*/middleware.use(function(req, res, next){    try{
       req.addon1 = 'I add something';  
    }catch(err){
       next(err);
    }
    next();
});//Add the second middleware.use(function(req, res, next){
     res.addon2 = 'I add something more';
     next();
});//Add the third middleware. use (function (req, res, next) {if (req. addon2) {delete req. addon2);
     }
     res.addon3 = 'I add something a lot';
     next();
});

IV. Classes of Definition of Consumption

"Consumption" is a recently learned word. It feels like X, so I'll install it here.~

let req = {};let res = {};let result = middleware.start(req,res);console.log(req, res);

V. View the results of the operation

Different results can be seen when errors occur and normal responses occur:

6. Running on the server side

It's too casual to start a web server with node~

const http = require('http');//The above stack of code http. createServer (function (req, res) {let result = {};
    middleware.start(req, result);
    res.end(JSON.stringify(result));
}).listen(9527);

Take a look at the effect (custom messages can be sent to the front desk when accessing the server):

Author: Dashi is silent.