ECE366 - Lesson 8
React
Instructor: Professor Hong
## What is React?
- Javascript library
- Created at Facebook
- Open-sourced in 2013
- Docs: [https://reactjs.org/docs/getting-started.html](https://reactjs.org/docs/getting-started.html)
## What is Javascript?
- High level, interpreted language
- Allows you to implement complex features on web pages
- Used with HTML and CSS (for styling)
- Logging: ```console.log();```
## Setup/Installation
- Add React Developer Tools from Chrome Extensions and add to chrome
- Inspect Element -> Components
- Can also install on Firefox
## React in Index.html
```
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<script
src="https://unpkg.com/react@17/umd/react.development.js"
crossorigin
></script>
<script
src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"
crossorigin
></script>
<title>React ⚛️</title>
</head>
<body>
<h1>Getting Started with React</h1>
</body>
</html>
```
## React in Index.html
```
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<script src="https://unpkg.com/react@17/umd/react.development.js" crossorigin></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.development.js" crossorigin></script>
<title>React ⚛️</title>
</head>
<body>
<div id="root"></div>
<script type="text/javascript">
ReactDOM.render(
React.createElement("h1", null, "Getting Started!"),
document.getElementById("root")
);
</script>
</body>
</html>
```
## ReactDOM.render
ReactDOM.render() - 2 arguments
- what to create: React.createElement("h1", null, "TEXT")
- where to put it: document.getElementById("root")
## Variable Names
```
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<script
src="https://unpkg.com/react@17/umd/react.development.js"
crossorigin
></script>
<script
src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"
crossorigin
></script>
<title>React ⚛️</title>
</head>
<body>
<div id="root"></div>
<script type="text/javascript">
let heading = React.createElement(
"h1",
{ style: { color: "blue" } },
"Heyyyy Everyone!"
);
ReactDOM.render(
heading,
document.getElementById("root")
);
</script>
</body>
</html>
```
## JSX, Babel
```
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<script src="https://unpkg.com/react@17/umd/react.development.js" crossorigin></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.development.js" crossorigin></script>
<script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
<title>React ⚛️</title>
</head>
<body>
<div id="root"></div>
<script type="text/babel">
ReactDOM.render(
<ul>
<li>🤖</li>
<li>🤠</li>
<li>🌝</li>
</ul>,
document.getElementById("root")
);
</script>
</body>
</html>
```
- Javascript XML; extension of JS for React JS
- Can access variables with {variable}
## More JSX syntax
```
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<script
src="https://unpkg.com/react@17/umd/react.development.js"
crossorigin
></script>
<script
src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"
crossorigin
></script>
<script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
<title>React ⚛️</title>
</head>
<body>
<div id="root"></div>
<script type="text/babel">
let robot = "🤖";
let cowboy = "🤠";
let moon = "🌝";
let name = "React";
ReactDOM.render(
<ul>
<li>{robot}</li>
<li>{cowboy}</li>
<li>{moon}</li>
<li>{name.toUpperCase()}</li>
<li>{name.length}</li>
</ul>,
document.getElementById("root")
);
</script>
</body>
</html>
```
## React Components
- A function that returns JSX and can be rendered in DOM
- Should use capital letter for component/function name
- Multiple React components should be wrapped into 1 component
- Can be used to display dynamic data
## Component Properties
- Add props argument to component functions
- A container where you can put any properties in the component
## Example with React Components and Image
```
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<script
src="https://unpkg.com/react@17/umd/react.development.js"
crossorigin
></script>
<script
src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"
crossorigin
></script>
<script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
<title>RPS</title>
</head>
<body>
<div id="root"></div>
<script type="text/babel">
function Header(props) {
return (
<header>
<h1>{props.name}'s RPS</h1>
</header>
);
}
function Main(props) {
return (
<section>
<img
height={200}
src="./rps.png"
alt="Rock Paper Scissors"
/>
<ul>
{props.users.map((user) => (
<li key={user.id}>
{user.title}
</li>
))}
</ul>
</section>
);
}
function Footer(props) {
return (
<footer>
<p>Copyright {props.year}</p>
</footer>
);
}
const users = [
"Alpha",
"Beta",
"Gamma",
];
const userObjects = users.map(
(user, i) => ({
id: i,
title: user
})
);
function App() {
return (
<React.Fragment>
<Header name="Cooperps" />
<Main
adjective="amazing"
users={userObjects}
/>
<Footer
year={new Date().getFullYear()}
/>
</React.Fragment>
);
}
ReactDOM.render(
<App />,
document.getElementById("root")
);
</script>
</body>
</html>
```
## Create React App
- Install nodejs - [https://nodejs.org/](https://nodejs.org/)
```
sudo apt update
sudo apt install nodejs
```
- ```node -v``` - to check node version
- ```npm -v``` - check npm version
- ```npx create-react-app rps```
- ```npm start```
## Important Parts
- package.json - dependencies - react, react-dom, react-scripts
- src/index.js - entry point of the application, main JS file
- renders App
- React.StrictMode - additional checks
- public/index.html - similar to index.html w/ all your JSX injected
```
npm install
npm start
```
## Javascript Destructuring
Allows you to get specific elements from an argument/props
```
function App({ myVariable }) {
return (
<div className="App">
<h1>{myVariable}</h1>
</div>
);
}
```
- Also Array destructuring allows you to get certain elements from an array
## Changing States with useState
App.js
```
import "./App.css";
import { useState } from "react";
function App() {
const [emotion, setEmotion] = useState("happy");
return (
<div className="App">
<h1>Current emotion is {emotion}</h1>
<button onClick={() => setEmotion("sad")}>
Sad
</button>
<button
onClick={() => setEmotion("excited")}
>
Excited
</button>
</div>
);
}
export default App;
```
## Side Effects with useEffect
```
import "./App.css";
import { useState, useEffect } from "react";
function App() {
const [emotion, setEmotion] = useState("happy");
const [secondary, setSecondary] =
useState("tired");
useEffect(() => {
console.log(`It's ${emotion} around here!`);
}, [emotion]);
useEffect(() => {
console.log(`It's ${secondary} around here!`);
}, [secondary]);
return (
<div className="App">
<h1>Current emotion is {emotion}</h1>
<button onClick={() => setEmotion("sad")}>
Sad
</button>
<button
onClick={() => setEmotion("excited")}
>
Excited
</button>
<h2>
Current secondary emotion is {secondary}.
</h2>
<button
onClick={() => setSecondary("grateful")}
>
Grateful
</button>
</div>
);
}
export default App;
```
- dependencyArray is the 2nd argument for useEffect
- No argument makes it called everytime
- Empty array makes it called once
## Fetching Data from Service
fetch is built into the browser to make an HTTP request to get data
```
import "./App.css";
import { useState, useEffect } from "react";
function App() {
const [data, setData] = useState(null);
useEffect(() => {
fetch(
`http://localhost:8080/api/users`
)
.then((response) => response.json())
.then(setData);
}, []);
if (data)
return (
<pre>{JSON.stringify(data, null, 2)}</pre>
);
return <h1>Data</h1>;
}
export default App;
```
## Update CORS in Spring Boot server
WebserviceController.java
```
@CrossOrigin
@GetMapping("/users")
```
## React Forms
useRef - a hook that is going to reach out to some UI element and get its value, doesn't re-render
```
import "./App.css";
import { useRef } from "react";
function App() {
const txtTitle = useRef();
const hexColor = useRef();
const submit = (e) => {
e.preventDefault();
const title = txtTitle.current.value;
const color = hexColor.current.value;
alert(`${title}, ${color}`);
txtTitle.current.value = "";
hexColor.current.value = "";
};
return (
<form onSubmit={submit}>
<input
ref={txtTitle}
type="text"
placeholder="color title..."
/>
<input ref={hexColor} type="color" />
<button>ADD</button>
</form>
);
}
export default App;
```
## React Forms with useState
re-renders at the end
```
import "./App.css";
import { useState } from "react";
function App() {
const [title, setTitle] = useState("");
const [color, setColor] = useState("#000000");
const submit = (e) => {
e.preventDefault();
alert(`${title}, ${color}`);
setTitle("");
setColor("#000000");
};
return (
<form onSubmit={submit}>
<input
value={title}
onChange={(event) =>
setTitle(event.target.value)
}
type="text"
placeholder="color title..."
/>
<input
value={color}
type="color"
onChange={(event) =>
setColor(event.target.value)
}
/>
<button>ADD</button>
</form>
);
}
export default App;
```
## Form Libraries
- formik
- react hook forms
## React Router
To install:
```
npm install react-router-dom
```
## Configuring the Router
App.js
```
import "./App.css";
function Home() {
return (
<div>
<h1>My Website</h1>
</div>
);
}
export function About() {
return (
<div>
<h1>About Us</h1>
</div>
);
}
export function Contact() {
return (
<div>
<h1>Contact Us</h1>
</div>
);
}
export function App() {
return <Home />;
}
```
## Configuring the Router
index.js
```
import React from 'react';
import ReactDOM from 'react-dom/client';
import './index.css';
import { App, About, Contact } from "./App";
import {
BrowserRouter,
Routes,
Route
} from "react-router-dom";
const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(
<BrowserRouter>
<Routes>
<Route path="/" element={<App />} />
<Route path="/about" element={<About />} />
<Route
path="/contact"
element={<Contact />}
/>
</Routes>
</BrowserRouter>,
);
```
## Adding Links to the Router
App.js
```
import "./App.css";
import { Link } from "react-router-dom";
function Home() {
return (
<div>
<nav>
<Link to="/about">About</Link>
<Link to="/contact">Contact</Link>
</nav>
<h1>My Website</h1>
</div>
);
}
export function About() {
return (
<div>
<nav>
<Link to="/">Home</Link>
<Link to="/about">About</Link>
<Link to="/contact">Contact</Link>
</nav>
<h1>About Us</h1>
</div>
);
}
export function Contact() {
return (
<div>
<nav>
<Link to="/">Home</Link>
<Link to="/about">About</Link>
<Link to="/contact">Contact</Link>
</nav>
<h1>Contact Us</h1>
</div>
);
}
export function App() {
return <Home />;
}
```
## STOMP
- Simple/Streaming Text Oriented Message Protocol
- Allows you to create an interactive web application
- The web is the STOMP client
- The service is the message broker
- Example from [https://spring.io/guides/gs/messaging-stomp-websocket/](https://spring.io/guides/gs/messaging-stomp-websocket/)
## Pre-initialized Spring Initializr
[Pre-initialized Initializr](https://start.spring.io/#!type=maven-project&groupId=com.example&artifactId=messaging-stomp-websocket&name=messaging-stomp-websocket&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.messaging-stomp-websocket&dependencies=websocket)
Additional pom.xml dependencies
```
<dependency>
<groupId>org.webjars</groupId>
<artifactId>webjars-locator-core</artifactId>
</dependency>
<dependency>
<groupId>org.webjars</groupId>
<artifactId>sockjs-client</artifactId>
<version>1.0.2</version>
</dependency>
<dependency>
<groupId>org.webjars</groupId>
<artifactId>stomp-websocket</artifactId>
<version>2.3.3</version>
</dependency>
<dependency>
<groupId>org.webjars</groupId>
<artifactId>bootstrap</artifactId>
<version>3.3.7</version>
</dependency>
<dependency>
<groupId>org.webjars</groupId>
<artifactId>jquery</artifactId>
<version>3.1.1-1</version>
</dependency>
```
## HelloMessage Class
HelloMessage.java
```
package com.example.messagingstompwebsocket;
public class HelloMessage {
private String name;
public HelloMessage() {
}
public HelloMessage(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
```
## Greeting Class
Greeting.java
```
package com.example.messagingstompwebsocket;
public class Greeting {
private String content;
public Greeting() {
}
public Greeting(String content) {
this.content = content;
}
public String getContent() {
return content;
}
}
```
## GreetingController Class
GreetingController.java
```
package com.example.messagingstompwebsocket;
import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.messaging.handler.annotation.SendTo;
import org.springframework.stereotype.Controller;
import org.springframework.web.util.HtmlUtils;
@Controller
public class GreetingController {
@MessageMapping("/hello")
@SendTo("/topic/greetings")
public Greeting greeting(HelloMessage message) throws Exception {
Thread.sleep(1000); // simulated delay
return new Greeting("Hello, " + HtmlUtils.htmlEscape(message.getName()) + "!");
}
}
```
## WebSocketConfig Class
WebSocketConfig.java
```
package com.example.messagingstompwebsocket;
import org.springframework.context.annotation.Configuration;
import org.springframework.messaging.simp.config.MessageBrokerRegistry;
import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker;
import org.springframework.web.socket.config.annotation.StompEndpointRegistry;
import org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurer;
@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
@Override
public void configureMessageBroker(MessageBrokerRegistry config) {
config.enableSimpleBroker("/topic");
config.setApplicationDestinationPrefixes("/app");
}
@Override
public void registerStompEndpoints(StompEndpointRegistry registry) {
registry.addEndpoint("/gs-guide-websocket").withSockJS();
}
}
```
## Index.html
src/main/resources/static/index.html
```
<!DOCTYPE html>
<html>
<head>
<title>Hello WebSocket</title>
<link href="/webjars/bootstrap/css/bootstrap.min.css" rel="stylesheet">
<link href="/main.css" rel="stylesheet">
<script src="/webjars/jquery/jquery.min.js"></script>
<script src="/webjars/sockjs-client/sockjs.min.js"></script>
<script src="/webjars/stomp-websocket/stomp.min.js"></script>
<script src="/app.js"></script>
</head>
<body>
<noscript><h2 style="color: #ff0000">Seems your browser doesn't support Javascript! Websocket relies on Javascript being
enabled. Please enable
Javascript and reload this page!</h2></noscript>
<div id="main-content" class="container">
<div class="row">
<div class="col-md-6">
<form class="form-inline">
<div class="form-group">
<label for="connect">WebSocket connection:</label>
<button id="connect" class="btn btn-default" type="submit">Connect</button>
<button id="disconnect" class="btn btn-default" type="submit" disabled="disabled">Disconnect
</button>
</div>
</form>
</div>
<div class="col-md-6">
<form class="form-inline">
<div class="form-group">
<label for="name">What is your name?</label>
<input type="text" id="name" class="form-control" placeholder="Your name here...">
</div>
<button id="send" class="btn btn-default" type="submit">Send</button>
</form>
</div>
</div>
<div class="row">
<div class="col-md-12">
<table id="conversation" class="table table-striped">
<thead>
<tr>
<th>Greetings</th>
</tr>
</thead>
<tbody id="greetings">
</tbody>
</table>
</div>
</div>
</div>
</body>
</html>
```
## app.js
src/main/resources/static/app.html
```
var stompClient = null;
function setConnected(connected) {
$("#connect").prop("disabled", connected);
$("#disconnect").prop("disabled", !connected);
if (connected) {
$("#conversation").show();
}
else {
$("#conversation").hide();
}
$("#greetings").html("");
}
function connect() {
var socket = new SockJS('/gs-guide-websocket');
stompClient = Stomp.over(socket);
stompClient.connect({}, function (frame) {
setConnected(true);
console.log('Connected: ' + frame);
stompClient.subscribe('/topic/greetings', function (greeting) {
showGreeting(JSON.parse(greeting.body).content);
});
});
}
function disconnect() {
if (stompClient !== null) {
stompClient.disconnect();
}
setConnected(false);
console.log("Disconnected");
}
function sendName() {
stompClient.send("/app/hello", {}, JSON.stringify({'name': $("#name").val()}));
}
function showGreeting(message) {
$("#greetings").append("| " + message + " |
");
}
$(function () {
$("form").on('submit', function (e) {
e.preventDefault();
});
$( "#connect" ).click(function() { connect(); });
$( "#disconnect" ).click(function() { disconnect(); });
$( "#send" ).click(function() { sendName(); });
});
```
## RPS Game Logic
- Add server side logic
- Add UI to communicate with server