Parimad reageerimisõpetused

React on JavaScripti kogu kasutajaliideste loomiseks. See valiti 2017. aasta Stack Overflow 2017. aasta arendajate uuringu kategoorias „Raamid, raamatukogud ja muud tehnoloogiad” kõige armastatumaks.

React on JavaScripti teek ja sellele ehitatud React-rakendused töötavad brauseris, EI serveris. Sellised rakendused suhtlevad serveriga ainult vajadusel, mis muudab need väga kiireks võrreldes traditsiooniliste veebisaitidega, mis sunnivad kasutajat ootama, kuni server terved lehed uuesti renderdab ja brauserisse saadab.

React kasutatakse kasutajaliideste loomiseks - mida kasutaja teie veebirakenduse kasutamiseks oma ekraanil näeb ja suhtleb. See liides on jaotatud komponentideks, selle asemel, et teil oleks üks tohutu leht, jagate selle väiksemateks osadeks, mida nimetatakse komponentideks. Üldisemalt öeldes nimetatakse seda lähenemist modulaarsuseks.

  • See on deklaratiivne: React kasutab deklaratiivset paradigmat, mis hõlbustab teie rakenduse üle otsustamist.
  • See on tõhus: React arvutab välja minimaalsed muudatused, mis on vajalikud teie DOM-i ajakohasena hoidmiseks.
  • Ja see on paindlik: React töötab teie juba tuttavate raamatukogude ja raamistikega.

Parimad õpetused reaktsiooni õppimiseks

freeCodeCampil on YouTube'is Reacti õpetus, mis õpetab kõik põhitõed vaid 5 tunni jooksul.

Meil on ka põhjalikum vaheline Reacti õpetus, mis õpetab Firebase'i abil tervet sotsiaalmeedia rakendust React üles ehitama. See on 12 tundi pikk ja kui te järgite seda, saate teada palju Reacti nõtkeid.

Miks õppida Reactit?

Reaktsioon hõlmab kompositsiooni, see tähendab palju komponente, mis mähivad funktsionaalsused kapseldatud konteinerisse.

Paljud populaarsed veebisaidid kasutavad Reactorit, rakendades MVC arhitektuurimustrit. Facebook (osaliselt), Instagram (täielikult), Khani akadeemia (osaliselt), New York Times (osaliselt), Yahoo Mail (täielikult), Dropboxi uus foto- ja videogaleriirakendus Carousel (täielikult) on populaarsed veebisaidid, mis teadaolevalt kasutavad React'i.

Kuidas need suured rakendused Reacti abil üles ehitatakse? Lihtne vastus on väikeste rakenduste või komponentide loomine. Näide:

const Component2 = () => { return ( ); }; const Component3 = () => { return ( ); }; const Component1 = () => { return ( ); }; ReactDOM.render( , document.getElementById("app") );

Reageerimine on enamasti deklaratiivne, mis tähendab, et me oleme rohkem huvitatud sellest, mida teha, mitte kuidas konkreetset ülesannet täita.

Deklaratiivne programmeerimine on programmeerimisparadigma, mis väljendab arvutuse loogikat kirjeldamata selle juhtimisvoogu. Deklaratiivsel programmeerimisel on teatud eelised, näiteks vähenenud kõrvalmõjud (ilmnevad siis, kui muudame olekut või muudame midagi või esitame API-taotluse), miinimumini viidud muutlikkus (kuna suur osa sellest on abstraktne), parem loetavus ja vähem vigu.

Reactil on ka ühesuunaline andmevoog. Reactori kasutajaliides on tegelikult riigi funktsioon. See tähendab, et oleku värskendamisel uuendab see ka kasutajaliidest. Nii et meie kasutajaliides areneb oleku muutumisel.

Reaktsiooni eelised

Mõned põhjused React'i kasutamiseks on:

  1. Kiire. Reactis tehtud rakendused saavad hakkama keerukate värskendustega ning tunnevad end siiski kiiresti ja reageerivalt.
  2. Modulaarne. Suurte, tihedate koodifailide kirjutamise asemel võite kirjutada palju väiksemaid korduvkasutatavaid faile. Reacti modulaarsus võib olla ilus lahendus JavaScripti hooldatavuse probleemidele.
  3. Skaalautuv. React töötab kõige paremini suurte programmide abil, mis kuvavad palju muutuvaid andmeid.
  4. Paindlik. Reacti saate kasutada huvitavate projektide jaoks, millel pole veebirakenduse tegemisega midagi pistmist. Inimesed alles mõtlevad välja Reacti potentsiaali. Uurimiseks on ruumi.

Virtuaalne DOM

Reakti maagia tuleneb DOM-i tõlgendamisest ja kasutajaliideste loomise strateegiast.

React kasutab HTML-puu praktiliselt kõigepealt renderdamiseks virtuaalset DOM-i. Seejärel iga kord, kui olek muutub ja saame uue HTML-puu, mis tuleb viia brauseri DOM-i, kirjutab kogu uus puu kirjutamise asemel React ainult uue puu ja eelmise puu vahe (kuna Reactil on mõlemad puud mälus). Seda protsessi nimetatakse puu lepitamiseks.

Lepitamine

Reactil on nutikas diferentseerimisalgoritm, mida ta kasutab oma DOM-sõlmes regenereerimiseks ainult seda, mida tegelikult tuleb regenereerida, samal ajal kui see hoiab kõik muu nagu on. See hajutamisprotsess on võimalik Reacti virtuaalse DOM-i tõttu.

Virtuaalse DOM-i abil hoiab React viimase DOM-i versiooni mälus. Kui sellel on brauserisse viimiseks uus DOM-versioon, on see uus DOM-versioon ka mälus, nii et React saab arvutada uue ja vana versiooni erinevuse.

Seejärel käsib React brauseril värskendada ainult arvutatud diffi, mitte kogu DOM-sõlme. Pole tähtis, mitu korda me oma liidest taastame, viib React brauserisse ainult uued “osalised” värskendused.

Reageerige kriimustustest

Kas soovite hakata reageerimise põhitõdesid õppima, ilma et peaksite arengukeskkonda looma? Võimalik, et kui olete veebiarenduses alles uus, võib arenduskeskkonna seadistamine tekitada veidi hirmu, kui proovite lihtsalt Reactit õppida.

Selles artiklis uurime, kuidas saaksime Reactiga alustada, kasutades ainult tekstiredaktorit ja brauserit ega midagi muud.

1 - seadistage Emmetiga katla plaadikood

Alustame 1. sammuga. Alustame oma brauseris olevast failist nimega “index.html”. Alustame katla plaadi HTML-koodiga. Kiireks alustamiseks soovitan kasutada Emmetit mis tahes tekstiredaktoriga, mis teil on. Esimesele reale sisestage html:5allpool oleva koodi saamiseks klahv Shift. Või võite jätkata ja altpoolt koodi kopeerida ja kleepida.

html:5

Selle tulemuseks on järgmine kood:

      Document    

Saame täita pealkirja “Aeg reageerida!”.

Seda sisu ei kuvata teie veebisaidil. Kõik HTML-faili pealkirja jaotises on metaandmed, mida meie brauser kasutab meie koodi tõlgendamiseks keha jaotises. See pealkiri kuvatakse meie lehe vahekaardil, mitte lehel.

2 - hankige skripti sildid, et rakendada reageerimisvõimalusi ja Paabeli raamatukogusid

Ok, item one is checked off of our list. Let’s look at item two. We are going to set up our developer environment by using script tags to bring in React and Babel.

This is not a real life developer environment. That would be quite an elaborate setup. It would also leave us with a lot of boiler plate code and libraries that would take us off subject of learning React basics. The goal of this series is to go over the basic syntax of React and get right into coding. We are going to use tags to bring in the React Library, the React DOM library (why), and the Babel library.

 ...       ... Time to React! 

You are free to use more updated versions of these libraries as they come out. They should not create any breaking changes for the content we are covering.

What are we doing here? The HTML element is used to embed or reference an executable script. The “src” attribute points to the external script files for the React library, ReactDOM library and Babel library.

This is like if you have an electric razor. It is literally no good to you no matter how fancy the electric razor unless you can plug it into the wall and gain access to electricity. Our React code we will write will be no good to us if our browser can’t plug into these libraries to understand and interpret what we are going.

This is how our application is going to gain the power of React, it is going to be how we insert React into the Dom. We have React and ReactDOM as two different libraries because there are use cases such as React Native where rendering to the DOM isn’t needed for mobile development so the library was split so people could decide what they needed depending on the project they were working on.

Because we will need our React to make it to the DOM we’ll use both scripts. Babel is how we take advantage of ECMA script beyond ES5 and deal with something called JSX (JavaScript as XML) that we will use in React. We’ll take a deeper look at the magic of Babel in an upcoming section :)

Alright, we have completed steps 1 and 2. We have set up our boiler plate code and set up our developer environment.

3 - Render React to the DOM

Our next two steps will be to choose our location within the DOM that we want to render our React content. And we'll use another script tag for our React content within the body. Generally, as a good separations of concerns practice, this would be in its own file then linked to this html document. We’ll do that later in upcoming sections. For now, we’ll let this dwell within the body of the html document we are currently in.

Now we are going to look at how simple it is to choose a place on the DOM to render our React content. We’ll go within the body. And best practice isn’t just to throw React into the body tag to be displayed but to create a separate element, often a div, that you can treat as a root element to insert your React content.

 React has not rendered yet 

We’ll create a simple element and give it an id of “app”. We are going to be able to target this location to insert our React content much the same way you might use CSS to target an id for styling of your choice. Any react content will be rendered within the div tags with the id of app. In the meantime we’ll leave some text saying that “React has not rendered yet”. If we see this when we preview our page it means that somewhere we missed rendering React.

Now, let’s go ahead and create a script tag within our body where we will create with React for the first time. The syntax we are going to need for our script tag is to add an attribute of “type”. This specifies the media type of the script. Above in our head we used an src attribute that pointed to the external script files for the React library, ReactDOM library and Babel library.

 React has not rendered yet 

The “type” of script that we are using will be wrapped in quotes and set to "text/babel". We’ll need the ability to use babel right away as we work with JSX.

First, we are going to render React to the DOM. We will use the ReactDOM.render() method to do this. This will be a method, and remember a method is just a function attached to an object. This method will take two arguments.

 React has not rendered yet ReactDOM.render(React What, React Where);  

The first argument is the “what” of React. The second argument is the “where” of the location you want it to be placed in the DOM. Let’s start by calling our ReactDOM.render() method. Our first argument is going to be our JSX.

 React has not rendered yet ReactDOM.render( 

Hello World

, React Where );

The official react docs state: “This funny tag syntax is neither a string nor HTML. It is called JSX, and it is a syntax extension to JavaScript. We recommend using it with React to describe what the UI should look like. JSX may remind you of a template language, but it comes with the full power of JavaScript. JSX produces React “elements.”

Often times, JSX freaks people out who have been developers for a while because it looks like HTML. At a very early age developers are taught separation of concerns. HTML has its place, CSS has its place and JavaScript has its place. JSX seems to blur the lines. You are using what looks like HTML but as Facebook says it comes with the full power of JavaScript.

This can freak out veterans, so many React tutorials start without JSX which can be quite complex. We won’t do that. Because this article is directed towards those who are very young in their careers you may not bring those red flags when you see this syntax.

And JSX is just really intuitive. You can probably quite easily read this code and see that this is going to be the largest header tag displaying the text “Hello World”. No mystery and pretty straightforward. Now, let’s look at what our second argument would be.

 React has not rendered yet ReactDOM.render( 

Hello World

, document.getElementById("app") );

This is where we want our React content rendered to the DOM. You’ve probably done this quite a few times in the past. We’ll just type in document.getElementById(). And we’ll pass into the argument of the id of app. And that is it. We will now target the div with the id of app to insert our React content.

We want to make sure our content is saved. Go ahead and open this up in the browser and you should see “Hello World”. As you can probably guess, using React is not the quickest or best way to create a Hello World app. We aren’t quite seeing the benefits of it yet. But now, we know that everything is working.

Go ahead and open up the console and look at the “elements”. You can do that on a Mac with command + shift + j or on Windows and Linux: Ctrl + Shift + J

If you click on the head tag, we can see our script libraries we included. Then we can go down to the body of our document. Let’s click on our div with the id of “app”. And when we do we see our

tag with the content “Hello World”.

View Entire Code Here.

Recap

So let’s do a quick recap. In our head tag we grabbed the script tags for React, ReactDOM and Babel. These are the tools our browser needs in its meta data to read our React code and JSX in specific.

We then located the position within the DOM that we wanted to insert our React by creating an element div with the id of “app”.

Next, we created a script tag to input our React code. We used the ReactDOM.render() method that takes two arguments. The “what” of the React content, in this case our JSX, and the second argument is the “where” that you want to insert the React content into the DOM. In this case it is the location with the id of “app”.

As an alternative to JSX, you can use ES6 and Javascript’s compiler like Babel. //babeljs.io/

Installing React

Creating a new React project

You could just embed the React library in your webpage like so2:

Smart programmers want to take the more practical and productive way: Create React App

npm install -g create-react-app create-react-app my-app cd my-app npm start

This will set up your development environment so that you can use the latest JavaScript features, provide a nice developer experience, and optimize your app for production.

npm start will start up a development server which allows live reloading3.

After you finish your project and are ready to deploy your App to production, you can just use npm run build to create an optimized build of your app in the build folder.

Your first React App

Installation

As specified in the previous section (Installation), run the Create React App tool. After everything has finished, cd into the folder of your application and run npm start. This will start a development server and you are all set to start developing your app!

npm install -g react-create-app create-react-app my-first-app cd my-first-app npm start

Editing the code

Start up your editor or IDE of choice and edit the App.js file in the src folder. When created with the react-create-app tool, there will already be some code in this file.

The code will consist of these parts:

imports

import React, { Component } from 'react'; import logo from './logo.svg'; import './App.css';

This is used by webpack to import all required modules so that your code can use them. This code imports 3 modules:

  1. React and Component, which allow us to use React as it should be used. (With components)
  2. logo, which allows us to use logo.svg in this file.
  3. ./App.css, which imports the stylesheet for this file.

classes/components

class App extends Component { render() { return ( 

Welcome to React

To get started, edit src/App.js and save to reload.

); } }

React is a library that makes use of Components, which let you split up your UI into independent, reusable pieces, and think about each piece in isolation. There is already 1 component created, the App component. If you used the create-react-app tool, this component is the main component in the project and you should build around this central class.

We will look at components in more detail shortly.

exports

When creating a class in React, you should export them after declaration, which allows you to use the component in another file by using the import keyword. You can use default after the export keyword to tell React that this is the main class of this file.

export default App;

View the results!

When you’ve started the development server by issuing the npm start command, you can view the changes you add to your project live in your browser. After issuing the command, npm should open a browser automatically displaying your app.

React - Components

Components are reusable in React. You can inject value into props as given below:

function Welcome(props) { return 

Hello, {props.name}

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

name="Faisal Arkan" will give value into {props.name} from the  function Welcome(props) and will return the component that has given value by name="Faisal Arkan". After that react will render the element into HTML.

Other ways to declare components

There are many ways to declare components when using React. There are two kinds of components, stateless components and stateful components.

Stateful

Class Type Components

class Cat extends React.Component { constructor(props) { super(props); this.state = { humor: 'happy' } } render() { return( 

{this.props.name}

{this.props.color}

); } }

Stateless Components

Functional Components (Arrow Function from ES6)

const Cat = props => { return ( 

{props.name}

{props.color}

; ); };

Kaudsed tagastuskomponendid

const Cat = props =>

{props.name}

{props.color}

;