{Concepts of React}

with redux to have better state management

Virtual DOM

“virtual”, representation of a UI is kept in memory and synced with the “real” DOM by a library such as ReactDOM

Set of instructions React follows when creating and updating User Interface

Using React

import React from 'react';
import ReactDOM from 'react-dom';

ReactDOM.render(
  React.createElement('h1', null, 'Heading'),
  document.getElementById('react-root')
);

<body>
 <div id="react-root">
 </div>
</body>

React elements

React.createClass - back in 2013

React functional component

React.Component

const todoList = React.createClass({
  displayName: 'TodoListItems',
  render() {
    return React.createElement('ul', {className: 'Todos'}, 
      React.createElement('li', null, 'Go to grocery shop'),
      React.createElement('li', null, 'Buy tequilla'),       
    );
  }
});

ReactDOM.render(
 React.createElement('TodoListItems', null, null),
 document.getElementById('react-root')
)

const TodoItemList extends React.Component {
  render() {
    const {items} = this.props;
    return React.createElement('ul', {className: 'Todos'}, 
	  items.map((item, i) => React.createElement('li', { key: i }, item)) }    
    );
  }
}

const todos = ['Go to Grocery Shop', 'Buy fruits', 'Get back home safely']l

ReactDOM.render(
 React.createElement('TodoListItems', {item: todos }, null),
 document.getElementById('react-root')
)

const TodoListItems = (props) => {
  return React.createElement('ul', {className: 'Todos'}, 
    React.createElement('li', null, 'Go to grocery shop'),
    React.createElement('li', null, 'Buy tequilla'),       
  );
}

JSX

Concise syntax for creating complex Dom Trees

<div className="container">
  <h1 className="page-title"> Todos for {this.props.username}
  <h3 className="sub-title"> { this.getSubtitle() } </h3>
  <ul>
    { this.props.items.map((item, i) => { return (<li key={i}> { item } </li>) }) }
  </ul>
  <a href="#" dataAttrs="data-attr-value" onClick=> link </a>
</div>

Props and inverse data flow

`defaultProps` to set default properties
`propTypes` for react layer properties validation

DOM reference of any child element using `ref` attribute. This is available in `this.refs`

const {_title} = this.refs.
const element = _this.current;

<h1 ref="_title"> Title </h1>

parent to child using props
child to parent using callback function


<parent sendToChild="data" reciveFromChild={callbackFn} />

<child onClick={(e) => {this.props.reciveFromChild(data)> { this.props.sendToChild } </child>

States

class App extends React.Component {
  constructor(props) {
    super(props);

    this.state = {
      title : "Hello World"
    }
  }

  changeTitle = (e) => {
    this.setState({
      title: 'New title'
    });
  };

  render() {
    const {title} = this.state;
    return(
    <>
      <h1> {title} </h1>
      <button onClick={this.changeTitle} > Change Title </button>
    </>
    );
  }
}

React lifecycle methods

componentDidCatch

componentWillMount

UNSAFE_componentWillMount

componentWillUpdate

UNSAFE_componentWillUpdate