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React JS intro
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Gabriele Petronella
September 30, 2015
Programming
3
390
React JS intro
A lightweight introduction to React JS in the context of web applications
Gabriele Petronella
September 30, 2015
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Transcript
AN INTRODUCTION TO REACTJS GABRIELE PETRONELLA SOFTWARE ENGINEER @ BUILDO
TWITTER: @GABRO27 / @BUILDOHQ
[email protected]
None
HTML
HTML <!DOCTYPE html> <html> <head> <title>This is a title</title> </head>
<body> <p>Hello world!</p> </body> </html>
I just had to take the hypertext idea and connect
it to the TCP and DNS ideas and — ta- da!— the World Wide Web — Tim Berners Lee
THE WEB, IN THE 90S ╔═══════════╗ ---------- ║ ║ gimme
dat page ║ ║----------------------> ║ browser ║ server ║ ║ <html>...</html> ║ ║<---------------------- ╚═══════════╝ ----------
None
<a href="/somewhere-fun">LINK!</a>
╔═══════════╗ ║ ║ gimme dat page ║
║----------------------> ║ ║ ║ ║ <html>...</html> ║ ║<---------------------- ║ browser ║ ... server ║ ║ ║ ║ do dat thing ║ ║----------------------> ║ ║ ║ ║ <html>...</html> ║ ║<---------------------- ║ ║ ╚═══════════╝
None
ADDING AN ELEMENT TO A CART <ul> <ul> <li>An apple</li>
<li>An apple</li> <li>A horse</li> ---> <li>A horse</li> </ul> <li>A dragon</li> </ul>
None
JAVASCRIPT (1995)
None
ADDING AN ELEMENT TO A CART var ul = document.getElementById("cart");
var li = document.createElement("li"); li.appendChild(document.createTextNode("Four")); ul.appendChild(li);
╔═══════════╗ ║ ║ gimme dat page ║
║----------------------> ║ ║ <html>...</html> ║ browser ║<---------------------- ║ ║ script.js ║ ║<---------------------- server ║ ║─────┐ ╚═══════════╝ ! ▲ ! <html>...</html>! !add item ! ! "########$ ! ! ! ! ! script !----- ! ! %########&
None
SO YOU SAY WE CAN CREATE HTML ELEMENTS...
SPA SINGLE-PAGE APPLICATIONS
╔═══════════╗ ║ ║ gimme dat page ║
║----------------------> ║ ║ <html>...</html> ║ browser ║<---------------------- ║ ║ app.js ║ ║<---------------------- ║ ╠─────┐ ╚═══════════╝ ! ▲ ! server <html>...</html>! !do stuff ! ! "##########$ ! ! !<----- ! ! gimme data ! app.js !----------------------> ! ! ! ! { data: "blah", ... } ! !<---------------------- %##########&
THE USUAL SUSPECTS
SOUNDS GREAT BUT...
COMPLEXITY!
MUTABLE STATE
OVER THE LAST 25 YEARS WE'VE SEEN...
FLUSH THE PAGE AT EVERY CHANGE VS COMPUTE THE CHANGES
LOCALLY
HERE'S HOW THE PAGE SHOULD LOOK LIKE VS HERE'S HOW
TO MAKE IT
IN OTHER WORDS...
DECLARATIVE VS IMPERATIVE
AND POTENTIALLY...
DEVELOPER EXPERIENCE VS USER EXPERIENCE
MEET REACT
DX + UX = REACT
DECLARATIVE APPROACH CONCEPTUALLY RE-RENDERING EVERYTHING EVERYTIME
IMPERATIVE EXPERIENCE MUTATION HAPPENS BEHIND THE SCENE
MVC
IT'S ALL ABOUT REUSABLE COMPONENTS
None
OUR FIRST COMPONENT const Hello = React.createClass({ render() { return
<div>Hello!</div>; } });
WAIT! HTML INSIDE JAVASCRIPT?!
YES, ALMOST...
JSX <div>Hello</div> gets translated to React.createElement("div", null, "Hello");
Details aside, there's no separation between templates and logic
SEPARATE CONCERNS NOT TECHNOLOGIES
ONLY TWO THINGS CAN AFFECT A COMPONENT > props !
> state "
PROPS ! A generalization over HTML attributes <button className='button inactive'>Click</button>
gets translated to React.createElement( "button", { className: 'button inactive' }, // <--- props "Click" );
OUR FIRST COMPONENT ACCEPTING PROPS const Greeter = React.createClass({ render()
{ return <div>Hello {this.props.name}!</div>; } ^ }); | just a javascript variable
AND THEN USE IT LIKE <Greeter name='Gabriele' /> ^ |_____________
passing a prop
CAN THIS BE EFFICIENT?
YOU WRITE render() { return ( <div> <span>Hello {this.props.userName}!</span> </div>
); }
REACT COMPUTES renderA: <div><span>Hello Gabriele!</span></div> renderB: <div><span>Hello Irina!</span></div> => [replaceAttribute
textContent 'Hello Irina'] ^ | | a state mutation, i.e. the horrible thing you want to avoid writing by hand
STATE ! A component can have an internal state AVOID
WHEN YOU CAN!
OUR FIRST STATEFUL COMPONENT !
const Counter = React.createClass({ getInitialState() { return { count: 0
}; }, increaseCount() { this.setState({ count: this.state.count + 1 }); }, ^ |_______________ triggers a re-render render() { return ( <div> <span>{this.state.count}</span> <button onClick={this.increaseCount}>Increase</button> </div> ); } });
THAT'S IT
REACT RECAP Everything is a component Components accept props Components
can have a state !
DEMO
THANKS
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