Better Middleware Use

What is middleware?

Middleware functions are functions that have access to the request object (req), the response object (res), and the next function in the application’s request-response cycle.

The next function is a function in the Express router which, when invoked, executes the middleware succeeding the current middleware.

The request-response cycle ends when you call res.send() or res.end().

Why middleware needed in the application?

• Execute any code on every request.
• Make changes to the request and the response objects.

Example

"use strict";

const express = require('express');

const app = express();

app.config = {
  PORT: 3000,
  ENV: process.env.NODE_ENV || 'development',
  HOST: '127.0.0.1'
};

const midOne = (req, res, next) => {
  console.log("midOne");
  next();
};

const midTwo = (req, res, next) => {
  console.log("midTwo");
  next();
};

app.use((req, res, next) => {
  console.log(1);
  next();
});

app.use((req, res, next) => {
  console.log(2);
  next();
});

app.get('/', [midOne, midTwo], (req, res) => {
  res.send("Root");
});

app.get('/home', [midOne, midTwo], (req, res) => {
  res.send("Home");
});

app.listen(8080, () => {
  console.log(app.config);
  console.log("Server is running on port 8080");
});

The global middleware will be called for each request. It’s better to keep clean, as minimum as use, always be async, avoid complex computation.

If any computation needed across multiple routes it should apply on routes.

Should or shouldn’t

• If any middleware performs based on some condition better to use condition outside middleware.

// bad
app.use((req, res, next) => {
  if (someCondition) {}
  else {}
  next();
});

// good
if (condition) {
  app.use((req, res, next) => {
    next();
  });
}

• Always add configuration/metadata outside middleware.

// bad
app.use((req, res, next) => {
  if (someCondition) {}
  else {}
  next();
});

// good
if (condition) {
  app.use((req, res, next) => {
    next();
  });
}

Here is the full source code: rjoydip-zz/better-middleware-use

Tags

JavaScript • Express • Middleware • Nodejs