React

Lesson 1

Agenda

History
About React
Introduction to JSX
Sample Component, dom.render
State
Components and Props
Rendering and render cycle
Installation

History

About React

Add React to web site

Manually modify .html
Manually build using ES6 modules (using tools like webpack or similar)
Automated using Create-React-App (or other start kits)

Manually add React

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <title>Add React in One Minute</title>
  </head>
  <body>

    <h2>Add React Blog in One Minute</h2>
    <p>This page demonstrates using React with no build tooling.</p>
    <p>React is loaded as a script tag.</p>

    <!-- We will put our React component inside this div. -->
    <div id="react_app_root"></div>

    <!-- Load React. -->
    <!-- Note: when deploying, replace "development.js" with "production.min.js". -->
    <script src="https://unpkg.com/react@16/umd/react.development.js" crossorigin></script>
    <script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js" crossorigin></script>

    <!-- Load our React component. -->
    <script src="blog.js"></script>

  </body>
</html>

index.html

Manually add React

'use strict';

const title = 'Hey, I have just joined React pro-camp';

const element = React.createElement(
      'div',
      {style: {color: 'darkorange'}},
      this.state.post.title
);

const reactRootDomNode = document.querySelector('#react_app_root');
ReactDOM.render(element, reactRootDomNode);

blog.js

Manually add React ES6

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

const title = 'Hey, I have just joined React pro-camp';

const element = React.createElement(
      'div',
      {style: {color: 'darkorange'}},
      this.state.post.title
);

const reactRootDomNode = document.querySelector('#react_app_root');
ReactDOM.render(element, reactRootDomNode);

blog.js

<!DOCTYPE html>
<html>
...
  <body>
    ...
    <div id="react_app_root"></div>
    ...
    <!-- Load React and our component. -->
    <script src="blog.js" type="module"></script>

  </body>
</html>

index.html

React ES6 + Builder

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

const title = 'Hey, I have just joined React pro-camp';

const element = React.createElement(
      'div',
      {style: {color: 'darkorange'}},
      this.state.post.title
);

const reactRootDomNode = document.querySelector('#react_app_root');
ReactDOM.render(element, reactRootDomNode);

blog.js

<script src="bundle.js"></script>

index.html

blog.js

Webpack

Rollup

Parcel, etc...

bundle.js (react, react-dom, blog.js)

Create React App

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

const title = 'Hey, I have just joined React pro-camp';

const element = React.createElement(
      'div',
      {style: {color: 'darkorange'}},
      this.state.post.title
);

const reactRootDomNode = document.querySelector('#react_app_root');
ReactDOM.render(element, reactRootDomNode);

index.js

>>> npx create-react-app my-blog
>>> cd my_blog
>>> npm run build

JSX

React createElement

const element = React.createElement(
               'div', {style: {color: 'darkorange'}}, 'My First Post'
);

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

const element = <div style={{color: 'darkorange'}}>'My First Post'</div>

const reactRootDomNode = document.querySelector('#react_app_root');
ReactDOM.render(element, reactRootDomNode);

HTML tag

(or React Component)

HTML attributes

(or React properties)

Content (children)

JSX

const element = <div>My First Post</div>;

const element = <div id="post-title">My First Post</div>;

const element = (<div id="post-title">
    My First Post
</div>);

const element = (<div id="post-title">
    <h1>My First Post</h1>
    <p>Hey, I have just started React pro-camp</p>
</div>);

JSX features

const user = { firstName: 'Viktor', lastName: 'Shevchenko'};

function formatName(user) {
    return user.firstName + user.lastName;
}

const element = <h1>Hello, {formatName(user)}</h1>;

Use {variableName} to access data from scope

JSX magic

In order to code with JSX syntax become a valid JavaScript code it has to be tranformed.

JSX

Transformer

TypeScript

Babel

JSX Transformation

const element = <div>My First Post</div>;

const element = React.CreateElement('div', null, 'My First Post');

JSX Transformation

const element = <div id="post-title">My First Post</div>;;

const element = React.CreateElement('div', {id: 'post-title'}, 'My First Post');

JSX Transformation

const element = (<div id="post-title">
    <h1>My First Post</h1>
    <p>Hey, I have just started React pro-camp</p>
</div>);

const element = React.CreateElement('div', {id: 'post-title'}, 
    React.CreateElement('h1', null, 'My First Post')
);

JSX Transformation

const element = (<div id="post-title">
    <h1>My First Post</h1>
</div>);

const element = React.CreateElement('div', {id: 'post-title'}, 
    React.CreateElement('h1', null, 'My First Post')
);

React Component

function Greeting(props) {
  return <h1>Hello, {props.name}</h1>;
}

class Greeting extends React.Component {
  render() {
    return <h1>Hello, {this.props.name}</h1>;
  }
}

Function

ES6 Class

const element = <Greetitg name="Viktor" />;

// the same as

const element = React.createElement(Greeting, {name: 'Viktor'}, null)

ReactDOM.render(element, document.getElementById('root'));

const element = {
    type: Greeting,
    props: {
        children: {
            type: 'h1',
            props: {
                children: 'Hello Viktor'
            }
        }
    }
}

React Component

Compose Components
Extract Components
Remember "props" - are read-only
! Do not create components inside other components

Component State

class Randomizer extends React.Component {
  constructor(props) {
    super(props);
    this.state = {count: Math.rand()};
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>Value is - {this.state.count}.</h2>
      </div>
    );
  }
}

ReactDOM.render(<Randomizer />, document.getElementById('root'));

// some time later

ReactDOM.render(<Randomizer />, document.getElementById('root'));

Component State

Do Not Modify State Directly
State Updates May Be Asynchronous
State Updates are Merged

Component Events

class Randomizer extends React.Component {
  constructor(props) {
    super(props);
    this.state = {count: Math.rand()};
  }

  reset(){
    this.setState({count: 0});    
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>Value is - {this.state.count}.</h2>
        <button onClick={this.reset}>Reset</button>
      </div>
    );
  }
}

this?

class Randomizer extends React.Component {
  constructor(props) {
    super(props);
    this.state = {count: Math.rand()};
    this.reset = this.reset.bind(this);
  }

  reset(e){
    this.setState({count: 0});    
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>Value is - {this.state.count}.</h2>
        <button onClick={(e) => this.reset(e)}>Reset</button>
      </div>
    );
  }
}

Component Lifecycle

Mounting/Unmounting

class Randomizer extends React.Component {
  constructor(props) {
    super(props);
    this.reset = this.reset.bind(this);
  }

  static getDerivedStateFromProps(props, state){
    // warning. Bad example.
    return !this.state.count && {count: props.count}
  }

  componentDidMount(){
    this.interval = this.setInterval(
      () => this.setState({count: Math.rand()}), 
      1000
    );
  }

  componentWillUnmount(){
    clearInterval(this.interval);
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>Value is - {this.state.count}.</h2>
        <button onClick={this.reset}>Reset</button>
      </div>
    );
  }
}

constructor()
static getDerivedStateFromProps()
render()
componentDidMount()

componentWillUnmount()

Component Lifecycle

Updating

class Randomizer extends React.Component {
  constructor(props) {
    super(props);
    this.reset = this.reset.bind(this);
  }

  shouldComponentUpdate(nextProps, nextState){
    if (nextProps.count === this.props.count) {
      return false;
    }
  }

  getSnapshotBeforeUpdate(prevProps, prevState) {
    
  }

  componentDidUpdate(prevProps, prevState, snapshot) {
    
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>Value is - {this.state.count}.</h2>
        <button onClick={this.reset}>Reset</button>
      </div>
    );
  }
}

static getDerivedStateFromProps()
shouldComponentUpdate()
render()
getSnapshotBeforeUpdate()
componentDidUpdate()

Component Lifecycle

Error Handling

class Randomizer extends React.Component {
  constructor(props) {
    super(props);
    this.state = {hasError: false}
  }

  static getDerivedStateFromError(error) {
    // Update component state
    return {hasError: true}
  }

  componentDidCatch(error, info) {
    // side effect, log error. 
  }

  render() {
    if(this.state.hasError) {
      return <h2>Error<h2>
    }

    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>Value is - {this.state.count}.</h2>
        <button onClick={this.reset}>Reset</button>
      </div>
    );
  }
}

static getDerivedStateFromError()
componentDidCatch()

React Magic

React Only Updates What’s Necessary
Reconciliation

Installataion

Create React App

Homework

Select theme
Deploy app

Lesson 2

Agenda

Lists and Keys
Conditional Rendering
Forms on Submit
Thinking in React

ReCap

What is React Element?
What is React Component?
difference between JSX and HTML?
How React Event is different

Lists and Keys

const MY_FILMS = [
    {
        name: 'Mad Max: Road of Fury',
        description: 'In a post-apocalyptic wasteland, a woman rebels against a 
            tyrannical ruler in search for her homeland with the aid of a group 
            of female prisoners, a psychotic worshiper, and a drifter named Max.',
        rating: 8.1
        tags: ['action', 'apocalyptic', 'post apocalypse', 'desert', 'australia', 'female warrior', 'chase']
    },
    {
        name: 'Logan',
        description: 'In a future where mutants are nearly extinct, an elderly and
            weary Logan leads a quiet life. But when Laura, a mutant child pursued
            by scientists, comes to him for help, he must get her to safety.',
        rating: 7.9
        tags: ['marvel comics', 'x men', 'superhero', 'mutant', 'reluctant hero']
    }

]

Lets build a list of elements based on array

Lists and Keys

render() {
    <div>
        {MY_FILMS.map(film => <div>{film.name}</div>)}
    </div>
}

Use ".map" Array method to render a list

Lists and Keys

What is key?

Special React property that gives elements stable identity
Used by React to track add, remove, change of elements in Array
Boost React performance by improving reconciliation
Eliminates enexpected data mixes up

Lists and Keys

keys in action

Array index

Unique id

<li key={0}>Mad Max</li>
<li key={1}>Logan</li>

<li key={1002}>Mad Max</li>
<li key={1003}>Logan</li>

this.setState([{name: 'Avangers'}, ...this.state.films]);

<li key={0}>Avangers</li>
<li key={1}>Mad Max</li>
<li key={2}>Logan</li>

<li key={1001}>Avangers</li>
<li key={1002}>Mad Max</li>
<li key={1003}>Logan</li>

keys are new!

keys are same!

li[0].textContent = 'Avangers'; // replace 'Mad Max'
li[0].textContent = 'Mad Max'; // replace 'Logan'

var li3 = document.createElement('li');
li3.textContent = 'Logan';

li.parentNode.appendChild(li3)

var li0 = document.createElement('li');
li0.textContent = 'Avangers';

li.parentNode.prependChild(li0)

Lists and Keys

Rules of Keys

Keys should be assigned to parent components (those in map function)
Prefer using unique id over an array indexes
keys is an internal React property, that is not passed to the inner component

Conditional Rendering

Conditional rendering

Using Regular "if else" Construction

function Rating ({hasVouted}) {

  if (hasVouted) {
    return <div>You have already rated this movie</div>
  }

  return (
    <div>Please rate this movie</div>    
  )
}

class Rating extends React.Component {
    
  render() {
    if (hasVouted) {
      return <div>You have already rated this movie</div>
    }

    return (
      <div>Please rate this movie</div>    
    )
  }
}

<Rating hasVouted={true} />

Conditional rendering

Define new Component variable

function Rating ({hasVouted}) {

  const RatingLabel = hasVouted ? <div>You have already rated this movie</div> : <div>Please rate this movie</div>  

  return (
    <RatingLabel />    
  )
}

Conditional rendering

Using &&

function Rating ({hasVouted}) {

  return (
    {!hasVouted && <div>Please rate this movie</div>}
  )
}

Conditional rendering

Using Ternary Operator

function Rating ({hasVouted}) {

  return (
    {hasVouted ? <div>You have already rated this movie</div> : <div>Please rate this movie</div>}     
  )
}

Conditional rendering

Avoid component render

<div />

<div></div>

<div>{false}</div>

<div>{null}</div>

<div>{undefined}</div>

<div>{true}</div>

Handling Events

Practical task

Implement selection on film when clicking on its name.

Display Selected Field Section only if any film is selected

Display description of selected film

Reimplement Selected movie to Edit Movie

Forms

Controlled Components

Control State - is kept and fully managed by React
Requires to have both value and onChange properties

How to avoid changes in the original component?

Forms

Uncontrolled Components

The state is managed by the browser
Relies on defaultValue prop

Task: Rebuild with uncontrolled components

"ref" prop

Special React only prop (like Key)
React.createRef() - to create a reference
May contain HTML Element, Component Instance
Not applicable to functional components

"ref" prop

Prefer "ref" over document.getElement...
Don't overuse refs
For example, instead of exposing open() and close() methods on a Dialogcomponent, pass an isOpen prop to it.
refs on components

Dom Manipulation

implement focus first field

Thinking in React

separate components
lift state up
There should be a single “source of truth”
If state involves writing more “boilerplate” code than two-way binding approaches
If something can be derived from either props or state, it probably shouldn’t be in the state.

Typechcking

prop-types
static type checking

Homework

style list
style form
write prop-types
make form edit independent from list item
implement cancel edit
implement image for movie

Lesson 3

Recap

why we need keys
why we need refs
how many ways to do conditional rendering
discuss homework

State Management

Dumb vs SmartComponents

Cross Component

Context

Child:

Child.contextTypes = {
  color: PropTypes.string
};

Parent:

getChildContext() {
    return {color: "purple"};
  }

Parent.childContextTypes = {
  color: PropTypes.string
};

Lesson 4

Code Reuse

techniques in React

Containment

class Tag extends React.Component {
  render() {
    return <pre>{this.props.tag}</pre>;
  }
}

{tags.map(tag => (
  <Tag key={tag} tag={tag} />
))}

function EmojiBlock(props) {
  return <span>{`🔥`}{props.children}{`🔥`}</span>
}

{tags.map(tag => (
  <EmojiBlock key={tag}><Tag tag={tag}/></EmojiBlock>
))}

Specialization

class Tag extends React.Component {
  render() {
    const {emoji, tag} = this.props;
    return <pre>{emoji}{tag}{emoji}</pre>;
  }
}

{tags.map(tag => (
  <Tag key={tag} tag={tag}/>
))}

function EmojiTag(props) {
    return <Tag {...props} />; 
}

{tags.map(tag => (
  <EmojiTag key={tag} tag={tag} emoji={`❤️`} />
))}

Reuse Statefull Logic

Inheritance

import React from "react";

export default class Emoji extends React.Component {
  constructor(props) {
    super(props);

    this.emojiList = ["🤟", "🔥", "⭐️", "🦄"];

    this.state = {
      emojiIdx: 0
    };
  }

  rotateEmoji = () => {
    const nextIndex = this.state.emojiIdx + 1;

    this.setState({
      emojiIdx: nextIndex === this.emojiList.length ? 0 : nextIndex
    });
  };

  render() {
    null;
  }
}

Inheritance

class EmojiTagInherited extends Emoji {
  render() {
    const emoji = this.emojiList[this.state.emojiIdx];

    return (
      <pre onClick={this.rotateEmoji}>
        {emoji}
        {this.props.tag}
        {emoji}
      </pre>
    );
  }
}

{tags.map(tag => (
  <EmojiTagInherited key={tag} tag={tag} />
))}

Inheritance

Pros

Cons

It works
1 React Element created

Inheritance complexity
Not a React way to do
Not applicable to function components

High Order Component

export default function withEmoji(WrappedComponent) {
  return class WithEmoji extends React.Component {
    constructor(props) {
      super(props);

      this.emojiList = ["🤟", "🔥", "⭐️", "🦄"];

      this.state = {
        emojiIdx: 0
      };
    }

    rotateEmoji = () => {
      const nextIndex = this.state.emojiIdx + 1;

      this.setState({
        emojiIdx: nextIndex === this.emojiList.length ? 0 : nextIndex
      });
    };

    render() {
      return (
        <WrappedComponent
          emoji={this.emojiList[this.state.emojiIdx]}
          rotateEmoji={this.rotateEmoji}
          {...this.props}
        />
      );
    }
  };
}

High Order Component

const TagWithEmoji = withEmoji(EmojiTag);


{tags.map(tag => (
  <TagWithEmoji key={tag} tag={tag} />
))}

{tags.map(tag => (
  <EmojiTag key={tag} tag={tag} />
))}

function EmojiTag({ tag, emoji = null, rotateEmoji = () => {} }) {
  return (
    <pre onClick={rotateEmoji}>
      {emoji}
      {tag}
      {emoji}
    </pre>
  );
}

HOC Questions

Mutation of the original component

class Film extends React.Component {
  render() {
    return (
      <div>
          Name: {this.props.name},
          Description: {this.props.description}      
      </div>
    );
  }
}

function withLogProps(Component) {
  InputComponent.prototype.componentDidUpdate = function(prevProps) {
    console.log('Previous props: ', prevProps);
    console.log('Current props: ', this.props);
  };
  
  return Component;
}

const FilmLogger = withLogProps(Film);

No more possible to use Film Component separately
Impossible to apply 2 mutational HOCs
Don't work with functional components

function logProps(Component) {
  return class extends React.Component {
    componentDidUpdate(prevProps) {
      console.log('Previous props: ', prevProps);
      console.log('Current props: ', this.props);
    }

    render() {

      return <WrappedComponent />;

    }
  }
}

      return <WrappedComponent {...this.props} />;

Always bypass unrelated props

HOC Questions

Maximizing Composability

const FilmLogger = withDebugLogProps(Film);

const FilmLogger = withLogProps(Film, 'debug');

const FilmLogger = withLogProps('debug')(Film);

function with one argument are easier to compose
can act as decorators

HOC Questions

HOC in render method

class FilmLogger extends React.Component {

  render() {
      const FilmWithLogging = withLogProps(Film);

      return (
        <FilmWithLogging />
      )
  }
}

do not use
cause performance degradation
remounting a component causes the state of that component and all of its children to be lost, React reconciliation process recreated a component tree each time
dynamically apply HOC in lifecycle methods

HOC Questions

HOC copy static methods

class Film extends React.Component {
  render() {
    return (
      <div>
          Name: {this.props.name},
          Description: {this.props.description}      
      </div>
    );
  }
}

Film.defaultProps = {
  name: 'Terminator',
  descriptions: 'Cyborg from future ..... '
}

const FilmLogger = withLogProps(Film);

FilmLogger.defaultProps ???

do copy
use hoistNonReactStatic

HOC Questions

HOC does not pass ref

class Film extends React.Component {
  render() {
    return (
      <div ref={this.props.ref}>
          Name: {this.props.name},
          Description: {this.props.description}      
      </div>
    );
  }
}

const FilmLogger = withLogProps(Film);

...


<FilmLogger ref={c => this.container = c}>

ref is a special property, like key
use React.forwardRef API (16.3+)

High Order Component

Pros

Cons

React way, use composition
cleaner code
Can be used as decorator

Has own rules
2 React Elements

Render Props

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

    this.emojiList = ["🤟", "🔥", "⭐️", "🦄"];

    this.state = {
      emojiIdx: 0
    };
  }

  rotateEmoji = () => {
    const nextIndex = this.state.emojiIdx + 1;

    this.setState({
      emojiIdx: nextIndex === this.emojiList.length ? 0 : nextIndex
    });
  };

  render() {
    return this.props.render({
      emoji: this.emojiList[this.state.emojiIdx],
      rotateEmoji: this.rotateEmoji
    });
  }
}

Render Props

function EmojiTag({ tag, emoji = null, rotateEmoji = () => {} }) {
  return (
    <pre onClick={rotateEmoji}>
      {emoji}
      {tag}
      {emoji}
    </pre>
  );
}

{tags.map(tag => (
  <EmojiRP key={tag} render={props => <EmojiTag tag={tag} {...props} />} />
))}

{tags.map(tag => (
  <EmojiRP key={tag} render={props => <EmojiTag tag={tag} />} />
))}


/* props = {emoji, rotateEmoji} */

Render Props

Pros

Cons

React way, use composition
cleaner code
Less rules, more obvious props passing

2 React Elements
Worse readability when applying several RP

That is it!

Lesson 5

Routing

HTML 5 history API
Routing concepts
Build Router
Solutions for routing

HTML History API

История

всегда была урла
но навигация - запрос к серверу
что если страници почти идентичны?

Решения

не менять url
но тогда нельзя попасть сразу на нужную страницу
# based url

Нужна ли url? EE задачи

It identifies a unique resource.
bookmarking
search engine can index it
copy and paste
url matter

Problem

нельзя поменять url без перезагрузки

HTML 5 History API

Основная идея - не менять принцип работы браузера - а дать API для управления url

HTML 4 History API

Navigation

window.history.back();

window.history.go(-1);

window.history.forward();

window.history.go(1);

var numberOfEntries = window.history.length;

HTML 5 History API

Manipulation

window.history.pushState({data: 'test'}, 'page 2', page2.html);

window.history.replaceState({data: 'test'}, 'page 2', page2.html);

window 'popstate' event

(window.onpopstate = funcRef;)

State - The state object is a JavaScript object which is associated with the new history entry

Title - title for the state to which you're moving

URL - The new history entry's URL. Understand when the browser does any server request

HTML 5 History API

pushState can accept any URL in the current domain vs only hash
You don't have to change the URL if you don't want to. When window.location preserves history only if the hash is the same
You can associate arbitrary data with your new history entry. With the hash-based approach, you need to encode all of the relevant data into a short string.
If the title is subsequently used by browsers, this data can be utilized (independent of, say, the hash).
pushState() never causes a "hashchange" event to be fired, even if the new URL differs from the old URL only in its hash.

Routing

Static vs Dynamic routing
Philosophy of dynamic routing
Routing Solutions
How To Treat Routing(source of state or result of state)

Routing

Static

Dynamic

centralized
defined before application render
predefined routes
big chunks code splitting
easy inspection

decentralized
defined during application is rendering
responsive routes
small chunks code splitting
more complex inspection

Routing

Aviator - Aviator is a front-end router built for modular single page applications. (Example).
Backbone - Backbone supplies structure to JavaScript-heavy applications by providing models with key-value binding and custom events, collections with a rich API of enumerable functions, views with declarative event handling, and connects it all to your existing application over a RESTful JSON interface.
component-router: Flux-based routing solution for components
Director - A tiny and isomorphic URL router for JavaScript.
Finch - A simple, yet powerful, javascript route handling library.
mvc-router Use the Model-View-Controller (MVC) pattern to build React applications.
react-mini-router A minimal URL router mixin.
react-passage: Passage helps when linking or redirecting to routes that may or may not be in your react app.
react-router - A popular declarative router for React
react-router-component Declarative routing.

Routing

'react-router-dom'
<BrowserRouter>
<Route path='/about' component={About}/>
<Link to='/'>Home</Link>
<NavLink to='/react' activeClassName='hurray'>React</NavLink>

Practice

Implement Router

Lesson 7

Agenda

Error Boundaries
React.memo
React.lazy
Suspense
Hooks

Error Boundaries

React components that catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI

Catch

Do Not Catch

render
lifecycle
constructors

event handlers
async code
server side rendering
error in Error Boundary component

Error Boundaries

componentDidCatch()

static getDerivedStateFromError()

Render a fallback UI

Log error information

Only class components can be error boundaries.
Declare an error boundary component once and use it throughout your application
The granularity of error boundaries is up to you(minimum top-level routes)
Errors that were not caught by any error boundary will result in unmounting of the whole React component tree

React.memo

What is React.PureComponent?

class ListOfInts extends React.PureComponent {
  render() {
    return <div>{this.props.ints.join(",")}</div>;
  }
}

const ListOfInts = React.memo(props => <div>{this.props.ints.join(",")}</div>)

const ListOfInts = React.memo(props => <div>{this.props.ints.join(",")}</div>, areEqualFunction)

*areEqualFunction - should return reversed from shouldComponentUpdate

React.lazy

CommonJS

AMD

Ecma2015

Techniques for importing code in JS?

https://github.com/tc39/proposal-dynamic-import

import('someOtherModule.js')
    .then(module => {
        module.loadPageInto(main);
    })
    .catch(err => {
        main.textContent = err.message;
    });

React.lazy

// Film.jsx

const Film = () => <div>Terminator</div>;

export default Film;

// App.jsx

import React, { lazy } from 'react';

const Film = lazy(() => import('./Film'));


class App extends React.Component {

 ...

  render() {
    return(
      <div>
        <h1>App with Films<h1>
        <Film>
      </div>
    );  
  }
}

React.Suspense

// App.jsx

import React, { lazy, Suspense } from 'react';

const Film = lazy(() => import('./Film'));


class App extends React.Component {

 ...

  render() {
    return(
      <div>
        <h1>App with Films<h1>
        <Suspense fallback={<h2>Films are loading<h2>}>
          <Film />
        </Suspense>
      </div>
    );  
  }
}

Concurrent React

ReactDOM.createRoot(document.getElementById('root')).render(<App />);

ReactDOM.render(<App />, document.getElementById('root'));

<Suspense fallback={<h2>Films are loading<h2>} maxDuration='500'>
  <Film />
</Suspense>

Suspense example

class Suspense extends React.Component {

  constructor(props) {
    super(props);

    this.state = {
      showFallbackUI: true;
    }
  }

  componentDidCatch(error) {
    if (error instanceOf Promise) {
        error.then(() => this.setState({showFallbackUI: false}))
    }
  }

  render() {
    return this.state.showFallbackUI ? this.props.fallback : this.props.children;
  }

}

Hooooooks

Motivation

It’s hard to reuse stateful logic between components
Complex components become hard to understand
Classes confuse both people and machines
Functional Components could not use statefull logic

Using Hooks

Backward compatible
Gradually adopted
opt-in

Hook in action

class RandomInt extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      ints: [5, 3, 8]
    };
    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    this.setState({
      ints: [...this.state.ints, 
                parseInt(Math.random() * 10, 10)
        ];
    });
  }

  render() {
    return (
      <div>
        <button 
          onClick={this.handleClick}
        >
            Add Random Int
        </button>
        <ListOfInts ints={this.state.ints} />
      </div>
    );
  }
}

import { useState } from 'react';

function RandomInt() {
  const [ints, setInts] = useState([]);

  return(
    <div>
      <button 
        onClick={setInts([...ints, 
                parseInt(Math.random() * 10, 10)])}
      >
          Add Random Int
      </button>
    <ListOfInts ints={ints} />
  </div>
  )
}

Types Of Hooks

Built in

Custom

useState
useEffect
useContext
useReducer
useCallback
useMemo
useRef

a function that contains a stateful logic and is used in React functional component. (starts with 'use')

useEffect

useEffect(() => {
    googleMap.panTo(props.coordinates)
});

componentDidMount

componentDidUpdate

useEffect(() => {
    document.addEventListener('click', handleDocumentClick);

    return () => {
        document.removeEventListener('click', handleDocumentClick)
    }
});

componentDidMount

componentDidUpdate

componentWillUnmount

useEffect(() => {
    document.addEventListener(props.event, handleDocumentClick);

    return () => {
        document.removeEventListener(props.event, handleDocumentClick)
    }
}, [props.event]);

componentDidMount

conditional componentDidUpdate

componentWillUnmount

useEffect(() => {
    document.addEventListener(props.event, handleDocumentClick);

    return () => {
        document.removeEventListener(props.event, handleDocumentClick)
    }
}, []);

componentDidMount

componentWillUnmount

useContext

function Link(props) {
  const router = useContext(RouterContext);
    
  return() {
    <a
      href=""
      onClick={e => {
        e.preventDefault();
        router.pushState({}, "", props.to);
      }}
    >
      {props.children}
    </a>
  }
}

export default class Link extends React.Component {
  render() {
    return (
      <RouterContext.Consumer>
        {router => (
          <a
            href=""
            onClick={e => {
              e.preventDefault();
              router.pushState({}, "", this.props.to);
            }}
          >
            {this.props.children}
          </a>
        )}
      </RouterContext.Consumer>
    );
  }
}

useRef

function Map() {
  const googleMap = useRef(null);

  render() {
    return (
      <Map
	item
	xs={12}
	style={style}
	google={google}
	onReady={(gm) => googleMap.current = gm }
	onClick={(e) => googleMap.current.panTo(e.coordinates)}
	zoom={10}
      />
    )
  }
}

class Map extends React.Component {
  ready(googleMap) {
    this.map = googleMap;
  }

  onMapClick(e) {
    this.googleMap.panTo(e.coordinates);
  }

  render() {
    return (
      <Map
	item
	xs={12}
	style={style}
	google={google}
	onReady={this.ready}
	onClick={this.onMapClick}
	zoom={10}
      />
    )
  }
}

Rules Of Hooks

Applied to only functional components
Order of hooks calls matters
Do not call in loops, conditions, nested functions
Call hooks from top level of React component
Call hooks inside other hooks
Start your custom hook with 'use'

React

Lesson 1

Agenda

History

About React

Add React to web site

Manually add React

Manually add React

Manually add React ES6

React ES6 + Builder

Create React App

JSX

React createElement

JSX

JSX features

JSX magic

JSX Transformation

JSX Transformation

JSX Transformation

JSX Transformation

React Component

Function

ES6 Class

React Component

Component State

Component State

Do Not Modify State Directly

State Updates May Be Asynchronous

State Updates are Merged

Component Events

Component Lifecycle

Mounting/Unmounting

Component Lifecycle

Updating

Component Lifecycle

Error Handling

React Magic

Installataion

Homework

Lesson 2

Agenda

ReCap

Lists and Keys

Lists and Keys

Lists and Keys

What is key?

Lists and Keys

keys in action

Lists and Keys

Rules of Keys

Conditional Rendering

Conditional rendering

Using Regular "if else" Construction

Conditional rendering

Define new Component variable

Conditional rendering

Using &&

Conditional rendering

Using Ternary Operator

Conditional rendering

Avoid component render

Handling Events

Handling Events

Practical task

Forms

Controlled Components

Forms

Uncontrolled Components

"ref" prop

"ref" prop

"ref" prop

Dom Manipulation

Thinking in React

Typechcking

Homework

Lesson 3

Recap

State Management

Cross Component

Parent to Child

'react-router-dom'