Intro

🙋‍♂️

Frontend engineer

9 years FE experience
AngularJS, Angular, Ember, React
currently at Productboard

❤️ 📸

Slides

https://slides.com/nuc

Remind me

look at your project
breaks!
lunch?

Setup IDE

Install

nodejs
- https://nodejs.org/en/
Visual Studio Code
- https://code.visualstudio.com
Quokka plugin
- VS Code ➡ extensions ➡ search for quokka

Let's talk about React! 👍

React

library for managing view
component based
- helps split the app into small pieces
used to create SPA

Client

Server

Database

HTTP

browser

request

html page

Client

Server

Database

HTTP

React in browser, mobile app...

API

request

data

Single page application

Web server

html, js

Create React app

CRA

tool for scaffolding react app

npx create-react-app my-app --template typescript

Important parts

package.json

describes the package
dependecies list
npm scripts

tsconfig.json

settings for typescript compiler
"target" = build for version of JS

/public folder

contains assets
index.html

index.tsx

renders React into HTML element

const root = ReactDOM.createRoot(
  document.getElementById('root') as HTMLElement
);
root.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>
);

App.tsx

the main component

NPM

Dependency management

Node package manager

packaging system
large repository 3rd party libs
https://www.npmjs.com

{
  "name": "my-package",
  "version": "1.0.0",
  "description": "This is just description of my awesome package",
  "main": "index.js",
  "scripts": {
    "dev": "nodemon --exec npm run start",
    "start": "tsc && node dist/index.js",
    "test": "mocha --opts mocha.opts"
  },
  "author": "Martin Nuc",
  "license": "ISC",
  "dependencies": {
    "@types/chai": "4.0.4",
    "@types/mocha": "2.2.43",
    "@types/node": "8.0.28",
    "@types/sinon": "2.3.4",
    "chai": "4.1.2",
    "mocha": "3.5.3",
    "nodemon": "1.12.1",
    "sinon": "3.2.1",
    "ts-node": "3.3.0",
    "typescript": "2.5.2"
  }
}

package.json

Scripts


"scripts": {
  "start": "react-scripts start",
  "build": "react-scripts build",
  "test": "react-scripts test",
  "eject": "react-scripts eject"
},

used to execute commands
npm dependencies executables resolution (from node_modules/.bin/*)

npm run <name>

Shortcut for start and test scripts only. For others you have to use npm run

Runs any script from npm.

npm start

npm test

👉

➡️ Start the React app

Dependencies

npm install lodash

installs lodash library:

npm install -D @types/lodash

installs lodash type definitions:

Use library in your code

import lodash from 'lodash';
lodash.difference([1, 2, 3], [2, 3]);

Dependencies and GIT

we don't commit dependencies
put node_modules folder in .gitignore
npm install to install dependencies

{
  "name": "my-package",
  "version": "1.0.0",
  "description": "This is just description of my awesome package",
  "main": "index.js",
  "scripts": {
    "dev": "nodemon --exec npm run start",
    "start": "tsc && node dist/index.js",
    "test": "mocha --opts mocha.opts"
  },
  "author": "Martin Nuc",
  "license": "ISC",
  "dependencies": {
    "@types/chai": "4.0.4",
    "@types/mocha": "2.2.43",
    "@types/node": "8.0.28",
    "@types/sinon": "2.3.4",
    "lodash": "4.17.5",
    "chai": "4.1.2",
    "mocha": "3.5.3",
    "nodemon": "1.12.1",
    "sinon": "3.2.1",
    "ts-node": "3.3.0",
    "typescript": "2.5.2"
  }
}

package.json

Semantic versioning

6.11.2

patch

minor version

major version

Semantic versioning

6.11.2

patch

minor version

major version

- major changes, breaks API

Semantic versioning

6.11.2

patch

minor version

- new features

- doesn't break API

major version

- major changes, breaks API

Semantic versioning

6.11.2

patch

- only bugfixes

minor version

- new features

- doesn't break API

major version

- major changes, breaks API

➡️ Use lodash

install lodash library (https://lodash.com)
work in index.tsx
use difference function from lodash find how are these array different:
- [1,2,3,4]
- [3,4,5,6]

JSX

Elements

const label = React.createElement('a', {
  href: 'https://google.com'
}, 'Go to Google.com');

<a href="https://google.com">Go to Google.com</a>

children

props

type

What is JSX?

syntactic sugar around createElement
almost like HTML
transpiled to Javascript
example in App.tsx:

import React from 'react';

function App() {
  return (
    <div className="App">
      Hello
    </div>
  );
}

function App() {
  return React.createElement('div', { className: 'App' }, 'Hello');
}

Q: Why className?

import React from 'react';

function App() {
  return (
    <div className="App">
      Hello
    </div>
  );
}

function App() {
  return React.createElement('div', { className: 'App'}, 'Hello');
}

Q: What happens now?

import React from 'react';

function App() {
  return (
    <div>
      Yes
    </div>
    <div>
      No
    </div>
  );
}

function App() {
  return ????????
}

Solution: React Fragment

like empty element
when you want to return multiple elements - wrap them in fragment

import React from 'react';

function App() {
  return (
    <>
      <div>
        Yes
      </div>
      <div>
        No
      </div>
    </>
  );
}

➡️ Before we continue

remove everything in the body of App.tsx component
notice the browser reloads

function App() {
  return <h1>Hello</h1>;
}

Print a variable

function App() {
  let something = 'hello';
  return <div>{something}</div>;
}

Print an array

function Array() {
  let array = [1,2,3];
  return <div>
    {array.map((item, index) => <span key={index}>{item}</span>)}
  </div>;
}

Components

Component

reusable unit
just a function
input
- ="props"
output
- React element

type Props = {
  name: string;
};

function NameComponent(props: Props) {
  return <h1>Hi, my name is {props.name}!</h1>;
}

ReactDOM.render(
  <NameComponent name="Martin" />,
  document.getElementById('root')
);

Component tree

split big problems to smaller ones

Component tree

Component

Component tree

Stateful components (smart)
- used to fetch data
- data manipulation
Stateless components (dumb)
- only display data
pass data down, emit events up

Component tree

Component

User info

ArticleList

Article

Today Weather

Article

I am smart 💡

Stateless component

everything to display is received via props
just a function
- input: props (=properties)
- output: React element
easy to test

function NameComponent(props) {
  return <h1>{props.name}</h1>;
}

How to use a component?

pass data down

function App() {
  return <NameComponent name="Martin" />
}

➡️ Dynamic table

create a component which displays a table using JSX
receives number of columns and rows as parameter

Hello	Hello	Hello	Hello
Hello	Hello	Hello	Hello
Hello	Hello	Hello	Hello

<Table columns={4} rows={3} />

Children props

you might pass HTML as body of element:

<Table columns={5} rows={2}>
  <h1>Hello</h1>
</Table>

Table component receives react element via children prop:

function Table(props) {
  return (
    <table>
      <tr>
        <td>
          {props.children}
        </td>
      </tr>
    </table>
  )
}

Event handling

React unifies API of events (link)

<button type="button" onClick={() => console.log('Hello')}>
  Hello world
</button>

State

useState

hook for storing data
instead of declaring variable

import React, { useState } from 'react';

function Counter() {
  const [name, setName] = useState('nobody');
	
  function handleGiveName(name: string) {
    setName(name);
  }

  return <div>
    My name is {name}.
    <button onClick={() => handleGiveName('Martin')}>
      Give me name
    </button>
  </div>
}

initial value

➡️ Create counter

create button with counter as text
start from 0
everytime you click the button the counter is increased

Conditions

use if statement
use ternary operator

render() {
  const random = Math.random();
  if (random < 0.5) {
    return <span>lower</span>
  } else {
    return <span>higher</span>
  }
}

render() {
  const random = Math.random();
  return <span>
    {random < 0.5 ? 'lower' : 'higher'}
  </span>
}

Styling app

CSS modules

scoped CSS
can use preprocessors (SCSS, SASS)

import styles from './App.module.css';

function Component() {
  return <div className={styles.red}>Hello</div>
}

.red {
  color: red;
}

App.module.css

App.tsx

Conditional styling

classnames library
npm i classnames @types/classnames
key = class to be applied
value = condition

import cn from 'classnames';
import styles from './App.module.css';

...

<div className={cn({ [styles.invalid]: this.state.invalid })}>
   
</div>

useEffect

hook for side effects
second argument say when it runs
- empty - on every render
- [ ] - only at the begining (=on mount)
- [ variable ] - only when variable changes
should return cleanup function

useEffect example

tracks mouse position

export const MyMouse = () => {
  const [mousePosition, setMousePosition] = useState({x: 0, y: 0});
  
  useEffect(() => {
    const onMouseMove = event => {
      setMousePosition({
        x: event.clientX,
        y: event.clientY
      });
    };
    window.addEventListener('mousemove', onMouseMove);
    
    return () => {
      window.removeEventListener('mousemove', onMouseMove);
    };
  }, []);
  
  const {x, y} = mousePosition;
  return (
    <div>My mouse x position is {x} and y position is {y}</div>
  );
};

Try useEffect

show text with mouse position
when the mouse position is
- on the left to the last click - change text to green color
- on the right to the last click - change text to red color

Create automatic counter

create component which increases counter every second
in parent component create button which shows/hides this component

Creating own event

component emits event up

type Props = {
  doWork: () => void;
};

function ChildComponent(props: Props) {
  handleClick = () => {
    this.props.doWork();
  }

  return <button onClick={this.handleClick}>emit event</button>;
}

<ChildComponent doWork={() => console.log('triggered')} />

parent component:

child component:

Create dropdown

What is dropdown?
button which opens menu when clicked

Controlled input

use component state as the only source of truth

funciton Component() {
  const [name, setName] = useState('nobody');
  const [inputName, setInputName] = useState(name);

  function handleGiveName() {
    setName(inputName);
  }

  return <>
    My name is {name}.
    <input
      value={inputName} 
      onChange={(e) => setInputName(e.target.value)} />
    <button onClick={() => handleGiveName()}>Give me name</button>
  </>
}

Create input

input of type number
how much the counter will increment

API request

Axios library

used to make http requests
npm install axios @types/axios
- import in code:

import axios from 'axios';

➡️ Let's make http request

open API request in browser to see structure of response
- https://api.chucknorris.io
display joke in the component
create a button to load another joke

GET https://api.chucknorris.io/jokes/random

Component tree

Component

User info

JokeFetcher

Joke

I am smart 💡

data down

Custom hooks

separate logic from view
no render
named use*
hooks to component lifecycle
clear API

useMouseMove

const useMouseMove = () => {
  const [mousePosition, setMousePosition] = useState({ x: 0, y: 0 });

  useEffect(() => {
    const onMouseMove = (event: any) => {
      setMousePosition({
        x: event.clientX,
        y: event.clientY,
      });
    };
    window.addEventListener('mousemove', onMouseMove);
    return () => {
      window.removeEventListener('mousemove', onMouseMove);
    };
  }, []);

  return { x: mousePosition.x, y: mousePosition.y };
};

mouse position example
- no input
- outputs x, y of mouse

Fetch joke component

encapsulate fetching joke logic into custom hook
think about API first

Debugging

Main tools

console.log
React dev tools
Chrome debugger

debugger;

Chrome dev tools

Network
Source
Performance
Application
React dev tools
- Components
- Profiler

Logging

Sentry.io
TrackJS

React Context

Context

"global" state for subtree of components
avoids passing lot of props
Provider + Consumer

const MyContext = React.createContext(false);

function App() {
  return <MyContext.Provider value={true}>
    <Component />
  </MyContext.Provider>;
}

function Component() {
  const value = useContext(MyContext);
  
  return <div>{value}</div>;
}

Encapsulate context

Provider component

const MyContext = React.createContext(false);

export function MyContextProvider({initialState, children}) {
  const [state, setState] = useState(initialState);
  
  const api = {
    value: state,
    changeValue: (newValue) => setState(newValue)
  };
  
  return <MyContext.Provider value={api}>
    {children}
  </MyContext.Provider>;
}

// used to read value from comopnent
export const useMyContext = () => useContext(MyContext);
const { value, changeValue } = useMyContext();

➡️ Dark & Light theme 🌗

style your components to support dark & light theme
create button to switch the theme

Render props

pass function as children
composition pattern

function Counter({children}) {
  const [counter, setCounter] = useState(0);
  
  function increment() {
    setCounter(counter + 1);
  }
  
  return <>{children({counter, increment})}</>
}
  
function MyComponent() {
  return <div>
    <Counter>
      {({counter, increment}) => <>
        <div>Counter value: {counter}</div>
        <button onClick={increment}>INC</button>
      </>}
    </Counter>
  </div>
}

Formik

library for forms
supports schema validation
- uses library yup
docs

const schema = yup.object().shape({
  email: yup.string().required().email(),
  age: yup.number().required().positive().integer()
})

const initialValues = {
  email: '',
  age: 0
}

export function MyForm() {
  return (
    <Formik
      initialValues={initialValues}
      validationSchema={schema}
      onSubmit={values => console.log(values)}
    >
      {({ handleSubmit }) => (
        <form onSubmit={handleSubmit}>
          <Field type="email" name="email" />
          <ErrorMessage name="email" component="div" />
          
          <Field type="number" className="error" name="age" />
          <ErrorMessage name="age" className="error" component="div"/>
          
          <button type="submit">
            Submit
          </button>
        </form>
      )}
    </Formik>
  );
}

➡️ Create form

think about any form and create it using formik
include validations

useRef

manipulate with DOM elements
object with mutable current property

function Component() {
  const inputRef = useRef(null);
  
  function handleClick() {
    inputRef.current.focus();
  }
  
  return <div>
    <input ref={inputRef} />
    <button onClick={handleClick}>Focus the input</button>
  </div>
}

useRef

expose something from component to parent
used to expose API by libraries

function Counter(props, ref) {
  const [counter, setCounter] = useState(0);

  useImperativeHandle(ref, () => ({
    reset: () => setCounter(0)
  }));
  
  function handleIncrement() {
    setCounter(counter+1);
  }
 
  return <div onClick={handleIncrement}>{counter}</div>;
}

const ResetableCounter = forwardRef(Counter);

function Component() {
  const counterRef = useRef();
  
  return <>
    <ResetableCounter ref={counterRef} />
    <button onClick={() => counterRef.current.reset()}>Reset</button>
  </>
}

Routing

React router

used to create multiple pages
install react-router-dom + type definitions
docs

Define pages and links

import { BrowserRouter, Routes, Route, Link } from "react-router-dom";

function App() {
  return (
    <BrowserRouter>
      <Link to="/">Home</Link>
      <Link to="/categories">About</Link>
      <Link to="/categories/animals">Joke about animals</Link>
      <Link to="/categories/history">Joke about history</Link>
      
      <Routes>
        <Route index path="/" element={<Home />} />
        <Route path="/categories" element={<JokeCategories />} />
        <Route path="/categories/:category" element={<Joke />} />
      </Routes>
    </BrowserRouter>
  );
}

everything must be inside of <Router>

Navigate

const navigate = useNavigate();

navigate('/categories');

either using <Link>
or using useNavigate() hook

Reading url parameters

import { useParams } from "react-router-dom";

function Joke() {
  const params = useParams();
  
  return (
    {params.category}
  );
}

Try routing

Create routes
- / -> categories list
- /categories/:category -> joke from category
load joke based on category
- https://api.chucknorris.io

Performance optimizations

Problem

lot of rerenders
every render creates new function, object etc
DOM operations are expensive

React.memo

rerenders component only on prop change

const JokeMemoized = React.memo(function Joke() {
  ...
});
  
 
<JokeMemoized />

useMemo

precompute value
for computation-expensive values
avoids main thread lock

const useFibonacci = (n) => {
  const result = useMemo(() => fibonacci(n), [n]);
  
  return result;
}
                         
function fibonacci(n) {
  return n < 1 ? 0
       : n <= 2 ? 1
       : fibonacci(n - 1) + fibonacci(n - 2)
}

useCallback

used to retain a single function reference
avoids problem with recreating handler every render

function Component({me}) {  
  const handleClick = useCallback(
    (name) => console.log(`Hello ${name} and ${me}`)
  , [me]);
  
  return <ExpensiveComponent onClick={handleClick} />;
}

➡️ Optimize Joke

won't get rerendered on theme change (=on context change)
no waste = useCallback for handlers