Nodejs

INTRODUCTION

What is Nodejs? javascript runtime environment running chrome's V8 javascript engine in background runs single-threaded, non-blocking, asynchronously programming, which is very memory efficient Node.js eliminates the waiting, and simply continues with the next request Nodejs is used to make real time applications like chat app because of it's high speed and non-blocking features

A typical nodejs development environment includes, Tools like nvm (node version manager), npm/yarn (package managers) and external modules installed using package managers

JS tutorial

https://learnxinyminutes.com/docs/javascript/ https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript

5 / 2;  // = 2.5 // Floor division Math.floor(5/2); // =2   // Exponentiation Math.pow(2,3); // =8   // There are three special not-a-real-number values: Infinity; // result of e.g. 1/0 -Infinity; // result of e.g. -1/0 NaN; // result of e.g. 0/0, stands for 'Not a Number'     // Other data types null; // deliberately assigned for a non-value initialization undefined; // uninitialized value   // There's also a boolean type. true; false;   // parsing a numeral string parseInt('123', 10); // 123 parseInt('010', 10); // 10 parseInt('11', 2); // 3   // Number.isNaN() to determine whether a given argument is a number or not Number.isNaN('1'); // false Number.isNaN(NaN); // true   //string operations 'hello'.length; // 5 'hello'.charAt(0); // "h" 'hello, world'.replace('world', 'mars'); // "hello, mars" 'hello'.toUpperCase(); // "HELLO"   // 0, empty strings (""), NaN, null, and undefined => false // rest others                                                               => true   // declaring variables let a; // = undefined const a   'hello' + ' world';  // "hello world"   // from left to right if string is added to a number string concatenation is performed '3' + 4 + 5;  // "345"  3 + 4 + '5'; // "75"   // comparisons 123 == '123'; // true 1 == true; // true 123 === '123'; // false 1 === true;    // false   for (let value of array) {   // do something with value }   for (let property in object) {   // do something with object property } // Objects // Type 1 let a = new Object(); // Object is defined in JS   // Type 2 (literal) let a = { name: "john fernandes", id: 1234 }   // Example and usage var obj = {   name: 'Carrot',   _for: 'Max', // 'for' is a reserved word, use '_for' instead.   details: {     color: 'orange',     size: 12   } };   obj.details.color; // orange obj['details']['size']; // 12   // Arrays // Type 1 var a = new Array(); a[0] = 'dog'; a[1] = 'cat'; a[2] = 'hen'; a.length; // 3   // Type 2 var a = ['dog', 'cat', 'hen']; a.length; // 3   // Looping through an array for (var i = 0; i < a.length; i++) {   // Do something with a[i] }   for (const currentValue of a) {   // Do something with currentValue }   // Array methods   a.toString() //Returns a string with the toString() of each element separated by commas.   a.join(sep) //Converts the array to a string — with values delimited by the sep param   a.pop() //Removes and returns the last item.   a.push(item1, ..., itemN) //Appends items to the end of the array.   a.shift() //Removes and returns the first item.   a.unshift(item1[, item2[, ...[, itemN]]]) //Prepends items to the start of the array.   a.slice(start[, end]) //Returns a sub-array.   a.sort([cmpfn]) //Takes an optional comparison function.   a.splice(start, delcount[, item1[, ...[, itemN]]]) //Lets you modify an array by deleting a section and replacing it with more items.   a.reverse() //Reverses the array.   // Functions function add(x, y) {   var total = x + y;   return total; }   //functions have an inbuilt array of arguments  function add() {   var sum = 0;   for (var i = 0, j = arguments.length; i < j; i++) {     sum += arguments[i];   }   return sum; } add(2, 3, 4, 5); // 14   // more efficient way function add(...args){    // do something with args array which can hold any number of arguments }   // Anonymous function var avg = function() {   var sum = 0;   for (var i = 0, j = arguments.length; i < j; i++) {     sum += arguments[i];   }   return sum / arguments.length; };   // Creating class objects using constructor function notation // note: this keyword function makePerson(first, last) {   return {     this.first: first,     this.last: last,     fullName: function() {       return this.first + ' ' + this.last;     },     fullNameReversed: function() {       return this.last + ', ' + this.first;     }   }; } var s = makePerson('Simon', 'Willison'); s.fullName(); // "Simon Willison" s.fullNameReversed(); // "Willison, Simon"   // exporting modules // type 1 - conventional // module.exports is an global object  function hello(){    //do something } module.exports = {    hello } // type 2 - ecma script for node versions >14 // using keyword exports  // refer blog https://www.freecodecamp.org/news/node-module-exports-explained-with-javascript-export-function-examples/

Getting Started

Download nodejs from https://www.nodejs.org Install an IDE

Hello World

  create a file names helloWorld.js  add a line 'console.log('Hello world');' to the file run the program using command '$ node helloWorld'

NPM

  nodejs package manager  packages can be classified as global and local Global packages are the packages installed in the system which can be accessed throughout the system these modules are stored in a directory defined while installation function as commandline tools as well Local packages are the packages used for managing project dependencies these modules are stored in node_modules directory within the project can function as commandline tools using npx $ npx local_package

npm commands $ npm install express $ npm install express@11.11.11 $ npm install -g express install latest express module if version not mentioned else the given version locally -g flag for global  $ npm install -i install all the dependencies mentioned in the package.json $ npm remove express deletes an installed package