Advance Topic in Express

What is advance topic?

• Middleware
• Configuration
• Debugging
• Templating Engines

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.

For example see below code

app.use(express.json()) // Middleware
.
.
.
app.delete('/api/courses/:id', (req, res) => {
    // Middleware
    pass
})

The diagram of above code is

Create Custom Middleware

app.use(function (req, res, next) {
    console.log("Loggg");
    next(); // it's important if you don't write the request processing pipline has got hange
})

Built-in Middleware

app.use(express.urlencoded({ extended: true })) // it's not usefull now 
app.use(express.static('public')) // this middleware for serve static files and argument is folder name

Third-party Middleware

We can read a complete list of third-party middleware in tis link

there are two common middleware:

• helmet: Helmet helps you secure your Express apps by setting various HTTP headers.
• morgan: HTTP request logger middleware for node.js

Note

Use middleware a lot is an effect on performance

Diffrent Environments

We want to set diffrent ENV for test, develope and production. we can do this with set env. the variable name for Environment is NODE_ENV. there are two ways to read this variable:

• process.env.NODE_ENV --> if not set return undifine
• app.get('env') --> if not set return development

Configuration

We use config package to handel our configuration in diffrent environment. For work with this package create folder that name is config and in this folder create json files of our configuration in each environment. For more information read document link

Debugging

We prefer to use debug package instead of console.log. It's work easily import package to file with require like below

const debug = require('debug')('app:test')// app:test is name space
// we can have multi debug in same file with diffrent name space

instead of use consol.log() in our code we use debug("..."). For specifid debug show in the consol or not use below command

export DEBUG=app:test
or
export DEBUG=

if you run faster you can use below command

DEBUG=app:test nodemon app.js

Templating Engines

Template is not use full now because a lot's of application use rest-ful api. The package that we use for template engine is pug.

Database Integration

We can use diffrent databases with nodejs and express for more information go to this link

Structure in Express App

In real wrold application we should have separate routes and middlewares in separate folder it's very important to have clean and maintainable code. In routes folder we have separate file for each entity and change code like this:

const express = require('express')
const router = express.Router();
router.get('/', (req, res) => {
    pass
});
...
module.export=router;

Summery

Express: Advanced Topics So, in this section, you learned that:

• A middleware function is a function that takes a request object and either terminates the request response cycle or passes control to another middleware function.

• Express has a few built-in middleware functions:

  • json(): to parse the body of requests with a JSON payload
  • urlencoded(): to parse the body of requests with URL-encoded payload
  • static(): to serve static files

• You can create custom middleware for cross-cutting concerns, such as logging, authentication, etc.

  Custom middleware (applied on all routes)

  JS

  Copy

  app.use(function(req, res, next)) {
  // ...
  next();
  }

  Custom middleware (applied on routes starting with /api/admin)

  JS

  Copy

  app.use(‘/api/admin’, function(req, res, next)) {
  // ...
  next();
  }

• We can detect the environment in which our Node application is running (development, production, etc) using process.env.NODE_ENV and app.get(‘env’).- The config package gives us an elegant way to store configuration settings for our applications.

• We can use the debug package to add debugging information to an application. Prefer this approach to console.log() statements.

• To return HTML markup to the client, use a templating engine. There are various templating engines available out there. Pug, EJS and Mustache are the most popular ones.