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React JS

What Is React?

React is a declarative, effective, and flexible JavaScript library for building user links. Allows you to compose complex UIs in small and isolated sections of code called “components”.

Why React?

React.js is a JavaScript library. It was developed by engineers at Facebook.

Here are just a few of the reasons why people choose to program with React:

Watch this excellent video explanation of the React Js.

Props and State

What are props?

Props are short for properties and they are used to pass data between React components. React’s the data flow between components is uni-directional (from parent to child only).

How do you pass data with props?

Here is an example of how data can be transferred using props:

What is state?

React has a special built-in object called state, which allows components to process and control their data. So unlike props, components cannot transfer data in a state, but they can create and control it internally.

Here is an example showing how to use state:

What are the differences between props and state?

· Components receive external data through props, while they can create and manage their data with state.

· Props are used for data transfer, and the state is for data management

· Data from props is read-only, and cannot be modified to the external component

· State data can be modified by its component, but is private (cannot be accessed externally)

· Modifying state must occur in setState () method

Lifecycle of Components

constructor

The constructor () method is named before anything else when the component is started, and it is the natural place to set up the initial state and other initial values. The constructor () method is called props.

render

The render () method is required and is the method that actually outputs the HTML to the DOM.

componentDidMount

The componentDidMount () method is called after the component is rendered. This is where you use the statements that require the component to already be placed in the DOM.

getDerivedStateFromProps

Also at an update, the getDerivedStateFromProps method is called. This is the first method when the component is updated. This is still a natural place to set a state object based on initial props.

shouldComponentUpdate

With shouldComponentUpdate () you can return a Boolean value that specifies whether the React should continue to be given or not. The default value is true.

componentDidUpdate

The componentDidUpdate method is called after the component update in the DOM. This action triggers an update phase, and since this component has a componentDidUpdate method, this method is used and writes the message in the empty DIV element.

componentWillUnmount

The componentWillUnmount method is called when the component is about to be removed from the DOM.

@babel/preset-react

Installation

npm install — save-dev @babel/preset-react

parcel

Installation

Create a node project.

npm init

Install parcel and babel-related dependencies.

npm install parcel@next –save-dev

Install React-related dependencies.

npm install react react-dom — save

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