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17 KiB
17 KiB
Conditional Rendering
As we can understand from the term, conditional rendering is a way to render different JSX or component at different condition. We can implement conditional rendering using regular if and else statement, ternary operator and &&. Let's implement a different conditional rendering.
Conditional Rendering using If and Else statement
In the code below, we have an initial state of loggedIn which is false. If the state is false we inform user to log in otherwise we welcome the user.
// index.js
import React from 'react'
import ReactDOM from 'react-dom'
// class based component
class Header extends React.Component {
render() {
const {
welcome,
title,
subtitle,
author: { firstName, lastName },
date,
} = this.props.data
return (
<header>
<div className='header-wrapper'>
<h1>{welcome}</h1>
<h2>{title}</h2>
<h3>{subtitle}</h3>
<p>
{firstName} {lastName}
</p>
<small>{date}</small>
<p>Select a country for your next holiday</p>
</div>
</header>
)
}
}
class App extends React.Component {
state = {
loggedIn: false,
}
render() {
const data = {
welcome: '30 Days Of React',
title: 'Getting Started React',
subtitle: 'JavaScript Library',
author: {
firstName: 'Asabeneh',
lastName: 'Yetayeh',
},
date: 'Oct 9, 2020',
}
// conditional rendering using if and else statement
let status
if (this.state.loggedIn) {
status = <h3>Welcome to 30 Days Of React</h3>
} else {
status = <h3>Please Login</h3>
}
return (
<div className='app'>
<Header data={data} />
{status}
</div>
)
}
}
const rootElement = document.getElementById('root')
ReactDOM.render(<App />, rootElement)
Let's add a method which allow as to toggle the status of the user. We should have a button to handle event for logging in and logging out.
// index.js
import React from 'react'
import ReactDOM from 'react-dom'
// A button component
const Button = ({ text, onClick, style }) => (
<button style={style} onClick={onClick}>
{text}
</button>
)
// CSS styles in JavaScript Object
const buttonStyles = {
backgroundColor: '#61dbfb',
padding: 10,
border: 'none',
borderRadius: 5,
margin: '3px auto',
cursor: 'pointer',
fontSize: 22,
color: 'white',
}
// class based component
class Header extends React.Component {
render() {
console.log(this.props.data)
const {
welcome,
title,
subtitle,
author: { firstName, lastName },
date,
} = this.props.data
return (
<header>
<div className='header-wrapper'>
<h1>{welcome}</h1>
<h2>{title}</h2>
<h3>{subtitle}</h3>
<p>
{firstName} {lastName}
</p>
<small>{date}</small>
</div>
</header>
)
}
}
class App extends React.Component {
state = {
loggedIn: false,
}
handleLogin = () => {
this.setState({
loggedIn: !this.state.loggedIn,
})
}
render() {
const data = {
welcome: '30 Days Of React',
title: 'Getting Started React',
subtitle: 'JavaScript Library',
author: {
firstName: 'Asabeneh',
lastName: 'Yetayeh',
},
date: 'Oct 9, 2020',
}
let status
let text
if (this.state.loggedIn) {
status = <h1>Welcome to 30 Days Of React</h1>
text = 'Logout'
} else {
status = <h3>Please Login</h3>
text = 'Login'
}
return (
<div className='app'>
<Header data={data} />
{status}
<Button text={text} style={buttonStyles} onClick={this.handleLogin} />
</div>
)
}
}
const rootElement = document.getElementById('root')
ReactDOM.render(<App />, rootElement)
How about if our condition is more than two? Like pure JavaScript we can use if else if statement. In general, conditional rendering is not different from pure JavaScript conditional statement.
Conditional Rendering using Ternary Operator
Ternary operator is an an alternative for if else statement. However, there is more use cases for ternary operator than if else statement. For example, use can use ternary operator inside styles, className or many places in a component than regular if else statement.
// index.js
import React from 'react'
import ReactDOM from 'react-dom'
// A button component
const Button = ({ text, onClick, style }) => (
<button style={style} onClick={onClick}>
{text}
</button>
)
// CSS styles in JavaScript Object
const buttonStyles = {
backgroundColor: '#61dbfb',
padding: 10,
border: 'none',
borderRadius: 5,
margin: '3px auto',
cursor: 'pointer',
fontSize: 22,
color: 'white',
}
// class based component
class Header extends React.Component {
render() {
const {
welcome,
title,
subtitle,
author: { firstName, lastName },
date,
} = this.props.data
return (
<header>
<div className='header-wrapper'>
<h1>{welcome}</h1>
<h2>{title}</h2>
<h3>{subtitle}</h3>
<p>
{firstName} {lastName}
</p>
<small>{date}</small>
</div>
</header>
)
}
}
class App extends React.Component {
state = {
loggedIn: false,
}
handleLogin = () => {
this.setState({
loggedIn: !this.state.loggedIn,
})
}
render() {
const data = {
welcome: '30 Days Of React',
title: 'Getting Started React',
subtitle: 'JavaScript Library',
author: {
firstName: 'Asabeneh',
lastName: 'Yetayeh',
},
date: 'Oct 9, 2020',
}
let status = this.state.loggedIn ? (
<h1>Welcome to 30 Days Of React</h1>
) : (
<h3>Please Login</h3>
)
return (
<div className='app'>
<Header data={data} />
{status}
<Button
text={this.state.loggedIn ? 'Logout' : 'Login'}
style={buttonStyles}
onClick={this.handleLogin}
/>
</div>
)
}
}
const rootElement = document.getElementById('root')
ReactDOM.render(<App />, rootElement)
In addition to JSX, we can also conditionally render a component. Let's change the above conditional JSX to a component.
// index.js
import React from 'react'
import ReactDOM from 'react-dom'
// A button component
const Button = ({ text, onClick, style }) => (
<button style={style} onClick={onClick}>
{text}
</button>
)
// CSS styles in JavaScript Object
const buttonStyles = {
backgroundColor: '#61dbfb',
padding: 10,
border: 'none',
borderRadius: 5,
margin: '3px auto',
cursor: 'pointer',
fontSize: 22,
color: 'white',
}
// class based component
class Header extends React.Component {
render() {
const {
welcome,
title,
subtitle,
author: { firstName, lastName },
date,
} = this.props.data
return (
<header>
<div className='header-wrapper'>
<h1>{welcome}</h1>
<h2>{title}</h2>
<h3>{subtitle}</h3>
<p>
{firstName} {lastName}
</p>
<small>{date}</small>
</div>
</header>
)
}
}
const Login = () => (
<div>
<h3>Please Login</h3>
</div>
)
const Welcome = (props) => (
<div>
<h1>Welcome to 30 Days Of React</h1>
</div>
)
class App extends React.Component {
state = {
loggedIn: false,
}
handleLogin = () => {
this.setState({
loggedIn: !this.state.loggedIn,
})
}
render() {
const data = {
welcome: '30 Days Of React',
title: 'Getting Started React',
subtitle: 'JavaScript Library',
author: {
firstName: 'Asabeneh',
lastName: 'Yetayeh',
},
date: 'Oct 9, 2020',
}
const status = this.state.loggedIn ? <Welcome /> : <Login />
return (
<div className='app'>
<Header data={data} />
{status}
<Button
text={this.state.loggedIn ? 'Logout' : 'Login'}
style={buttonStyles}
onClick={this.handleLogin}
/>
</div>
)
}
}
const rootElement = document.getElementById('root')
ReactDOM.render(<App />, rootElement)
Conditional Rendering using && Operator
The && operator render the right JSX operand if the left operand(expression) is true.
// index.js
import React from 'react'
import ReactDOM from 'react-dom'
// A button component
const Button = ({ text, onClick, style }) => (
<button style={style} onClick={onClick}>
{text}
</button>
)
// CSS styles in JavaScript Object
const buttonStyles = {
backgroundColor: '#61dbfb',
padding: 10,
border: 'none',
borderRadius: 5,
margin: '3px auto',
cursor: 'pointer',
fontSize: 22,
color: 'white',
}
// class based component
class Header extends React.Component {
render() {
console.log(this.props.data)
const {
welcome,
title,
subtitle,
author: { firstName, lastName },
date,
} = this.props.data
return (
<header style={this.props.styles}>
<div className='header-wrapper'>
<h1>{welcome}</h1>
<h2>{title}</h2>
<h3>{subtitle}</h3>
<p>
{firstName} {lastName}
</p>
<small>{date}</small>
</div>
</header>
)
}
}
const Login = () => (
<div>
<h3>Please Login</h3>
</div>
)
const Welcome = (props) => (
<div>
<h1>Welcome to 30 Days Of React</h1>
</div>
)
class App extends React.Component {
state = {
loggedIn: false,
techs: ['HTML', 'CSS', 'JS'],
}
handleLogin = () => {
this.setState({
loggedIn: !this.state.loggedIn,
})
}
render() {
const data = {
welcome: '30 Days Of React',
title: 'Getting Started React',
subtitle: 'JavaScript Library',
author: {
firstName: 'Asabeneh',
lastName: 'Yetayeh',
},
date: 'Oct 9, 2020',
}
// We can destructure state
const { loggedIn, techs } = this.state
const status = loggedIn ? <Welcome /> : <Login />
return (
<div className='app'>
<Header data={data} />
{status}
<Button
text={loggedIn ? 'Logout' : 'Login'}
style={buttonStyles}
onClick={this.handleLogin}
/>
{techs.length === 3 && (
<p>You have all the prerequisite courses to get started React</p>
)}
{!loggedIn && (
<p>
Please login to access more information about 30 Days Of React
challenge
</p>
)}
</div>
)
}
}
const rootElement = document.getElementById('root')
ReactDOM.render(<App />, rootElement)
In the previous section, we used alert box to greet people and also to display time. Let's render the greeting and time on browser DOM instead of displaying on alert box.
// index.js
import React from 'react'
import ReactDOM from 'react-dom'
// class based component
class Header extends React.Component {
render() {
console.log(this.props.data)
const {
welcome,
title,
subtitle,
author: { firstName, lastName },
date,
} = this.props.data
return (
<header style={this.props.styles}>
<div className='header-wrapper'>
<h1>{welcome}</h1>
<h2>{title}</h2>
<h3>{subtitle}</h3>
<p>
{firstName} {lastName}
</p>
<small>{date}</small>
</div>
</header>
)
}
}
const Message = ({ message }) => (
<div>
<h1>{message}</h1>
</div>
)
const Login = () => (
<div>
<h3>Please Login</h3>
</div>
)
const Welcome = (props) => (
<div>
<h1>Welcome to 30 Days Of React</h1>
</div>
)
// A button component
const Button = ({ text, onClick, style }) => (
<button style={style} onClick={onClick}>
{text}
</button>
)
// TechList Component
// class base component
class TechList extends React.Component {
render() {
const { techs } = this.props
const techsFormatted = techs.map((tech) => <li key={tech}>{tech}</li>)
return techsFormatted
}
}
// Main Component
// Class Component
class Main extends React.Component {
render() {
const {
techs,
greetPeople,
handleTime,
loggedIn,
handleLogin,
message,
} = this.props
console.log(message)
const status = loggedIn ? <Welcome /> : <Login />
return (
<main>
<div className='main-wrapper'>
<p>Prerequisite to get started react.js:</p>
<ul>
<TechList techs={this.props.techs} />
</ul>
{techs.length === 3 && (
<p>You have all the prerequisite courses to get started React</p>
)}
<div>
<Button
text='Show Time'
onClick={handleTime}
style={buttonStyles}
/>{' '}
<Button
text='Greet People'
onClick={greetPeople}
style={buttonStyles}
/>
{!loggedIn && <p>Please login to access more information about 30 Days Of React challenge</p>}
</div>
<div style={{ margin: 30 }}>
<Button
text={loggedIn ? 'Logout' : 'Login'}
style={buttonStyles}
onClick={handleLogin}
/>
<br />
{status}
</div>
<Message message={message} />
</div>
</main>
)
}
}
// CSS styles in JavaScript Object
const buttonStyles = {
backgroundColor: '#61dbfb',
padding: 10,
border: 'none',
borderRadius: 5,
margin: '3px auto',
cursor: 'pointer',
fontSize: 22,
color: 'white',
}
// Footer Component
// Class component
class Footer extends React.Component {
constructor(props) {
super(props)
}
render() {
return (
<footer>
<div className='footer-wrapper'>
<p>Copyright {this.props.date.getFullYear()}</p>
</div>
</footer>
)
}
}
class App extends React.Component {
state = {
loggedIn: false,
techs: ['HTML', 'CSS', 'JS'],
message: 'Click show time or Greet people to change me',
}
handleLogin = () => {
this.setState({
loggedIn: !this.state.loggedIn,
})
}
showDate = (time) => {
const months = [
'January',
'February',
'March',
'April',
'May',
'June',
'July',
'August',
'September',
'October',
'November',
'December',
]
const month = months[time.getMonth()].slice(0, 3)
const year = time.getFullYear()
const date = time.getDate()
return `${month} ${date}, ${year}`
}
handleTime = () => {
let message = this.showDate(new Date())
this.setState({ message })
}
greetPeople = () => {
let message = 'Welcome to 30 Days Of React Challenge, 2020'
this.setState({ message })
}
render() {
const data = {
welcome: '30 Days Of React',
title: 'Getting Started React',
subtitle: 'JavaScript Library',
author: {
firstName: 'Asabeneh',
lastName: 'Yetayeh',
},
date: 'Oct 9, 2020',
}
return (
<div className='app'>
<Header data={data} />
<Main
techs={techs}
handleTime={this.handleTime}
greetPeople={this.greetPeople}
loggedIn={this.state.loggedIn}
handleLogin={this.handleLogin}
message={this.state.message}
/>
<Footer date={new Date()} />
</div>
)
}
}
const rootElement = document.getElementById('root')
ReactDOM.render(<App />, rootElement)
Exercises
Exercises: Level 1
- What is conditional rendering?
- How do you implement conditional rendering?
- Which method of conditional rendering do you prefer to use?
Exercises: Level 2
- Make a single page application which changes the body of the background based on the season of the year(Autumn, Winter, Spring, Summer)
- Make a single page application which change the body of the background based on the time of the day(Morning, Noon, Evening, Night)
Exercises: Level 3
- Fetching data takes some amount of time. A user has to wait until the data get loaded. Implement a loading functionality of a data is not fetched yet. You can simulate the delay using setTimeout.
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