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 what is DOM? Document Object Model is representation of html elements in the form tree of JavaScript object.  For example  {html:{head: {title:{value:'Welcome to my website'}, body:{h1:{value: 'Cat Photo App'}}}  using Javascript we can modify it. let h1 = document.getElementByTagName('h1'); // {value:'Cat'} h1.value = 'Cat Lovers App' // we modified the DOM Using JavaScript , jQuery, developers having making website this way.   Problems with this type of Development: 1.  slow rendering issues: every modification of element is costly 2. It's hard to keep track of changes :   ReactJS introduced Virtual DOM   Virtual DOM is representation of real DOM.  It makes us feel as we are creating a entire new Real DOM. Everytime there is any change in Virtual DOM.  There is change in Virtual DOM (like timer update, button clicked). React uses Algorithms to update subtrees of Virtual DOM. After that new Virtual DOM is mounted on Real DOM. Is re-creating

WealthSimulator In this project in which user can buy and sell stocks virtually.   Requirements Basic Javascript Knowledge Text editor Node js https://nodejs.org/en/download/ 1. Setting up     Create a Folder named "WealthSimulator"    open   Terminal or Powershell inside the Folder  npm init -y // To Setup project   npm install express   Create a file server.js   server.js import express to your code create instance of express  Our app will send 'Welcome' text as a response  to request made with '/' in browser.  This will make app to listen to request at port Now we are all set to run our server Got to Terminal or power shell inside project folder npm start http://localhost:3000/ Cool Now, Our server is answering to request made by browser. 2. Yahoo Finance API npm install axios Make account on Rapid API Rapid API Subscribe to this API for free On Endpoints Tab Look for this in indices (left panel) Copy The code snippet and paste it server.js After  const app

 What is Express ? This is the Javascript framework that speeds up the process of building and deploying web applications. There is no real meaning in this definition other than words I recall reading in books and articles How express changed how I do things? As we learn how to code, we solve problems and construct things, but they are isolated solutions. Typical examples include a login form, virtual keyboard, or todolist. As I made this, I felt incomplete (I am still learning Javascript). When I reload the page, everything was null. No tasks in the todo list, no data in the virtual keyboard, and the login form is just a template. i attempted to make Habitica clones with vanilla Javascript. it works, but was a mess from files, folders, and code. the code is on github.  link Major things I wanted to do but cannot with Vanilla Javascript. Store some data. Organized Project (with proper links that always work) Error Handling   Like this Other people's API in project  Express has all

 The Problem The count of odd numbers between two non-negative integers low and high (inclusively) is given by low and high. Leet Code Problem 1523