Basic-Node

Single thread can manage multiple connections

Because, non-blocking I/O model

What is non-blocking I/O model

When we run nodejs in sarver it's perticuler one thread can handel many connections.    
Let suppose, I run a process which is I/O bound mean's wait for database excutor fatch so it's doesn't block thread and wait for a callback. When that particular I/O bound resolved a event fired.    

What is nmp?

nmp stands for node package manager.

why use [npm init] command

This utility will walk us through creating a package.json file.

What is Expressjs?

Express is a flexible Node.js web application framework that provides a strong set of features for web and mobile applications.

How to install Express in myapp directory and save it in the dependencies list?

$ npm install express

To install Express temporarily and not add it to the dependencies list:

$ npm install express --no-save

How to uninstall express

$ npm uninstall express

What is nodemon?

nodemon is a tool that helps develop Node.js based applications by automatically restarting the node application   when file changes in the directory are detected

Install nodemon in our system path globally:

$ npm install -g nodemon

Install nodemon as a development dependency:

$ npm install --save-dev nodemon

How to uninstsll?

$ npm uninstall nodemon

After download nodemon in your system if you get error like [nodemon : File C:\Users\user\AppData\Roaming\npm\nodemon.ps1 cannot be loaded because running scripts is disabled on this system. For more information, see about_Execution_Policies at https:/go.microsoft.com/fwlink/?LinkID=135170.]

1. Open PowerShell (Run As Administrator)  
2. Check the current execution policy using this command  
    Get-ExecutionPolicy
    # You should get 'Restricted'
3. Run this command to make it 'Unrestricted'  
    Set-ExecutionPolicy Unrestricted  
4. Check again whether execution policy changed by running this command  
    Get-ExecutionPolicy
    # You should get 'Unrestricted'
5. Now try to run nodemon on your project  
    nodemon 'filename.js'  

How to import-export in CommonJS module?

From second.js to first.js  

(second.js)---
function Simple(){
console.log("Hello World");
}
module.exports = Simple;

(first.js)---
const Simple = require("./second.js");
Simple();  

How to use ES6 module?

STEP-1: go to package.json file and add   "type":"module", after "author":"Teuton",  

STEP-2: add file name with mjs (first.mjs).