Express Series 2 : Middleware
Introduction
In this series we wanna talk about middleware in Express. Basicaly Middleware is a function which can access HTTP request (req) and HTTP responses (res) because middleware hook inside routing object.
If the current middleware function does not end , it must call **next() **to tell express for execute next middleware function .
We can use middleware that we create by our self or we can use third party middlware that express support it like body-parser, cookie parser etc. Generally middleware is put inside app.use() or router.use() method . This is some type of express middleware :
| Description | Middleware |
|---|---|
| Error handling middleware | app.use(err,req,res,next) |
| Built-in middleware | express.static, express.json , express.urlencoded |
| Thirdparty middleware | bodyparser , cookieparser etc. |
Writting Middleware
Before we writing a middleware , the most important thing is we must know the app.use() structure , because most of the time , middleware will put inside the app.use() method , here is the structure :
app.use(“path”,callback(http methods))
| Argument | Description |
|---|---|
| Path | A string representing a path |
| callback | A middleware function |
Writing Third party Middleware
Pretty Easy if you writing third party middleware , after you install & require the package from npm , you just write :
const express = require("express")
const app = express()
const cookieParser = require("cookie-parser")
const cors=require("cors")
const bodyparser=require("body")
// load the middleware
app.use(cookieParser())
app.use(cors())
app.use(bodyParser.urlencoded({ extended: false }));
That’s it very easy , and if you see why bodyparser have a parameters, it’s because body parser having that ability , too see what parameters or what third party middleware that express have you can check express offical , link down below :
Writing Custom Middleware
For Custom middleware i will show you 2 ways to do that , first inside same file and second in diferent file , for example i’ll make 2 middleware , first request log middleware and execute next middleware to the get date middleware and the last response to “/“ route . if we not call “next” on that 2 middleware we will not arrive to the “/“ route.
// Middleware
app.use((req, res, next) => {
console.log(req);
next();
});
app.use((req, res, next) => {
let date = new Date(Date.now()).toLocaleString();
console.log(date);
next();
});
app.get("/", (req, res) => {
res.send("Welcome Home");
});
For making more modular we can write in diferent file and export it , for example we have 2 file , index.js (for server) & midd.js (for main middleware).
midd.js
module.exports=function(){
return(req,res,next)=>{
let today=new.Date();
let hh=today.getHours();
let nn=today.getMinutes();
let ss=today.getSeconds();
let time=hh+':'+nn+':'+ss;
console.log(time);
}
}
index.js
const require("./midd.js")
app.use(midd())
app.use("/",(req,res)=>{
res.send("Welcome To HomePage")
})
Last Word
That’s all about basic middleware , this is very important , because we will use middleware all the time in node js for convert our logic and problem solving , i Hope you understand the basic , As always dont forget to check the documentation :