ExpressJS.txt

Request processing pipeline


const express = require("express");
const app = express();

* app.use(express.json()); = It reads the request body and it will parse the body of the request into a json object and then it will set OR populates req.body property.
* app.use(express.urlencoded({extended: true})); = It parses incoming requests with urlencoded payloads
* app.use(express.static('public')); = It is used to serve static files of the application

* If we use unnecesary middlewares, it will slow down the "request processing pipeline"

* In express, every route function is technically a middleware function

* A middleware function basically a function that takes request object and either return a response to the client or passes control to another middleware function.

* Every request we get on the server will go through the middleware function

* 







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Environments:
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* We can know the environment as
-> process.env.NODE_ENV
-> app.get('env'); = This will return "development" by default if "process.env.NODE_ENV" is not set explicitly.

* We can set environment variables as below.
-> If it is windows, "set NODE_ENV=production"
-> If it is linux, "export NODE_ENV=production"

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Configuration settings:
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* We should use "config" module/package
* There is another module as "rc", but we use "config".
* After installing "config", we should create "config" folder in root directory.
* Then need to create 3 json files, which are 
->default.json ->development.json ->production.json

* Usage
const config = require('config');
console.log('Application name'+ config.get('name'));
console.log('Application name'+ config.get('mail.host'));

* We should not store applicartion secret things like passwords, secret keys in config file.
We should create an environment variable and then read/call them in config file.

* To store/create environment variables, follow below process
-> If it is windows, "set appName_password=1234"
-> If it is linux, "export appName_password=1234"

Then need to create a file in "config" folder with the name "custom-environment-variables.json"
Ex: {
		"name": "My App - Production",
		"password": "appName_password"
	}

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Debugging:
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* We can use "debug" module/package to controll console.log messages and all that stuff
* After installation
const startupDebugger = require('debug')('app:startup'); - orbiraty namespace
const dbDebugger = require('debug')('app:db'); - orbiraty namespace

startupDebugger("This is startup message");
dbDebugger("This is Database related message");

* We can set what kind of dubugging information we can see in the console
Now we need to set environment variable
set DEBUG=app:startup,app:db
(OR) We can use wildcard to show all msgs
set DEBUG=app:*

We can remove above thing as 
set DEBUG=

We can also set them as
DEBUG=app* nodemon index.js
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