React was Developed at FB.

Dan was one of the developer

It is Library not a framework

ReactJS was developed to solve the Phantom message problem.

In FB the notification bell used to display the number of new messages. When It was opened and read the message still it was showing the same.

There are no SYNC between DOM and STATE

To solve this problem ReactJS was developed.

React provides a consistent sync between states and DOM.

It creates VIRTUAL DOM.

The HTML file contains a single root div element. Hence it is difficult for SEO

function render(reactElement,rootElement)
{
    const domElement = document.createElement(reactElement.type);
    domElement.innerHTML = reactElement.children;
    for( prop in reactElement.props)
    {
        domElement.setAttribute(prop, reactElement.props[prop])
    }
    rootElement.appendChild(domElement);

}
const rootElement = document.querySelector("#root");

// In React Library we have React.createElement(types,{props},Evaluated Expressions) funtion
const reactElement = {
    type:'a',
    props:{
        href:"<https://google.com>",
        target:"_blank"
    },
    children: "Click me"
}
render(reactElement,rootElement);