Lær reagere ved at opbygge en meme-generator

Memes er gode - de er sådan en sjov måde at beskrive ideer og meninger på. Så det er ikke tilfældigt, at jeg valgte en meme generator-app som hovedsten-projektet i mit gratis React-kursus på Scrimba. Appen fungerer ved at trække et tilfældigt meme-billede fra en API og placere din tekst over toppen af ​​det for at oprette din helt egen, personlige meme.

Så i denne artikel giver jeg dig en trinvis vejledning til oprettelse af appen. Hvis du nogensinde bliver forvirret, kan du også følge disse trin i Scrimba-kurset fra denne forelæsning.

Og hvis du kan lide min undervisningsstil og har lyst til en hårdere udfordring, når du har gennemført denne tutorial, så tjek mit kommende avancerede kursus om Scrimba.

Bemærk: Du bør allerede være ret fortrolig med nogle af de grundlæggende begreber i React, som komponenter, tilstand, rekvisitter og livscyklusmetoder. Også denne tutorial bruger ikke kroge, men i mit kommende kursus vil vi dække kroge i dybden og få masser af praksis med at bruge dem.

1. Oprettelse af kogepladen og gengivelse af en App-komponent

Oprettelse af kogepladens opgave

Den første ting, vi skal gøre, er at oprette kogepladekoden til appen. For at gøre dette importerer Reactog ReactDOMbruger vi ReactDOMtil at gengive en komponent kaldet App, som vi opretter senere. Vi sætter derefter Appkomponenten ved 'rod'. Vi importerer også Appfra dens fil "./App", som vi opretter om kort tid.

// index.js import React from 'react'; import ReactDOM from 'react-dom'; import App from './App'; ReactDOM.render(, document.getElementById('root')); 

Vi opretter derefter vores App.jsfil. I det opretter vi en funktionel komponent kaldet Appsom for nu returnerer en simpel

. Vi eksporterer den derefter. Det

giver os mulighed for at kontrollere, at appen vises korrekt på skærmen.

import React from 'react'; function App() { return 

Hello world!

; } export default App;

Det resulterende output er dette:

Gengivet Hello World

2. Oprettelse af Header- og MemeGenerator-komponenter

Oprettelse af header- og MemeGenerator-opgaven

Derefter opretter vi komponenterne Header og MemeGenerator. Overskriften viser kun elementer, mens MemeGenerator kalder til API'en og bevarer dataene i tilstand.

Lad os starte med at oprette Header.jsfilen. Da header er en komponent, der kun bruges til at vise, skal den være en funktionel komponent. Indtil videre skal komponenten returnere en simpel

. Efter oprettelsen eksporterer vi derefter header.

import React from 'react'; function Header() { return 

HEADER

; } export default Header;

Next, we create the MemeGenerator.js file. As the MemeGenerator component will be holding data and making calls to an API, it needs to be a class component. We still need to import React, and since it is going to be a class component, we'll import Component as well (which is a named import).

MemeGenerator needs a constructor() which calls super() and as it will be holding state, we add some empty state to it now. Like in the Header component, we render a simple

to start with. We then export MemeGenerator.

import React, { Component } from 'react'; class MemeGenerator extends Component { constructor() { super(); this.state = {}; //empty state } render() { return 

MEME GENERATOR SECTION

; } } export default MemeGenerator;

Now, we import both Header and MemeGenerator into App.js and create an instance of each one in our App component. In order to display the components correctly, we wrap them in a .

import React from 'react'; import Header from './Header'; import MemeGenerator from './MemeGenerator'; function App() { return ( ); } export default App; 

3. Completing the Header component.

To complete the component, we add a trollface image by inserting an tag and setting the src to the image's URL. We then add a

tag with the name of our app and wrap them both in the semantic HTML5 tag.

function Header() { return (  Problem?

Meme Generator

); }

As styling is outside the scope of this course, the CSS styles have already been created and applied to the tag. The result is this:

Rendered Header

That said, learners can always play around with the styling and hone their CSS skills by themselves. With the now complete, the rest of the challenge will take place in

4. Initializing state

Initialisering af tilstandsopgave

We now have to initialize state so that it saves a top text, a bottom text and a random image, which is already supplied.

To do this, we build up the empty object we placed in the when we originally built it. We initialize topText and bottomText as empty strings and randomImg as the provided URL.

class MemeGenerator extends Component { constructor() { super(); this.state = { topText: '', bottomText: '', randomImg: '//i.imgflip.com/1bij.jpg' }; } } 

5. Making the API call

Foretagelse af API-opkaldsopgave

Next, we make an API call to the provided URL and save the data returned (which is an array found in response.data.memes) to a new state property called allMemeImgs.

When we need to load data from an endpoint to use in our component, a good place to make the request is the componentDidMount() lifecycle method. As soon as the component mounts, we use the native fetch() function to call to the provided URL.

componentDidMount() { fetch("//api.imgflip.com/get_memes") } 

This returns a promise which we turn into a Javascript object with the .json() method.

componentDidMount() { fetch("//api.imgflip.com/get_memes") .then(response => response.json()) } 

Then we get the response which is useful to us by pulling the memes array from response.data.

componentDidMount() { fetch("//api.imgflip.com/get_memes") .then(response => response.json()) .then(response => { const { memes } = response.data }) } 

Now, we save the results to a new state property called allMemeImgs. To do this, we initialize allMemeImgs as an empty array.

this.state = { topText: '', bottomText: '', randomImg: '//i.imgflip.com/1bij.jpg', allMemeImgs: [] }; 

Now, back in componentDidMount(), we set state. As we are not interested in what the previous state was, we set allMemeImgs to memes.

componentDidMount() { fetch("//api.imgflip.com/get_memes") .then(response => response.json()) .then(response => { const { memes } = response.data this.setState({ allMemeImgs: memes }) }) } 

To ensure that it works, we console.log the first item, which looks something like this:

console.log output

Here's an overview of the entire componentDidMount() function.

componentDidMount() { //ensure that data is fetched at the beginning fetch("//api.imgflip.com/get_memes") //call to URL .then(response => response.json()) //turn promise into JS object .then(response => { const { memes } = response.data //pull memes array from response.data console.log(memes[0]) // check data is present this.setState({ allMemeImgs: memes }) // set allMemeImgs state }) } 

6. Creating the input form

We now want to create a form which will eventually allow the user to input the top and bottom texts. We do this with an HTML tag and a simple which says 'Gen'. We style it with the pre-provided CSS.

render() { return ( Gen ) } 

Rendered Gen-knap

7. Adding input fields to the form

Tilføjelse af inputfelts opgave

Next, it is up to us to add the two input fields (one for the top text and one for the bottom text). The form should be a controlled form, so we will need to add all the attributes needed in order for that to work. We will create the onChange handler later.

We create two input fields which both have the type text and appropriate name attributes (topText and bottomText). Rather than using labels, we use placeholders: 'Top Text' and 'Bottom Text'.

Lastly, in order to make this a controlled form, we set the value as equal to the current value in state with {this.state.topText} and {this.state.bottomText}.

render() { return ( Gen ) } 

8. Creating the onChange handler.

Oprettelse af onChange-handleropgaven

Now, we create the onChange handler, which will update the corresponding state on every change of the input field.

First, we create a handleChange() function which receives an event.

handleChange(event) { } 

Now, we set the onChange of both input fields to equal handleChange.

   Gen  

We need to remember to bind the method in the constructor — a common gotcha for React developers.

constructor() { super() this.state = { topText: "", bottomText: "", randomImg: "//i.imgflip.com/1bij.jpg", allMemeImgs: [] } this.handleChange = this.handleChange.bind(this) } 

To test the new handleChange() function, we add a simple console.log:

handleChange(event) { console.log("Working!") } 

If it is correctly firing, you'll see something like this:

Rendered console.log (

Now to fill in the handleChange() function. To do this, we want to pull the name and value properties from event.target so that we can get the name of the state we are supposed to update (topText or bottomText) and the value which is typed into the box.

handleChange(event) { const { name, value } = event.target } 

We will now use these to update state. As we are not interested in what the previous state was, we can just provide an object in which we set the [name] to the value typed into the input field.

handleChange(event) { const {name, value} = event.target this.setState({ [name]: value }) } 

9. Displaying a meme image alongside the top and bottom text

We now want the app to display a meme image alongside the top and bottom text. We insert an tag underneath the and set the randomImg which we initialized as its source by using src={this.state.randomImg}. We then add two

tags which display the corresponding text which is also saved in state. All of this is wrapped in a div and styled with the pre-provided meme class.

{this.state.topText}

{this.state.bottomText}

We can now test the app by typing into the text boxes. As state is being correctly set on every keystroke, the text displayed on the image changes each time we type.

Gengivet eksempel på fremskridt hidtil

10. Displaying a random meme image alongside the Top and Bottom text

Viser en tilfældig meme-billedopgave

Now, we need to create a method which displays a meme image which it randomly chooses from our allMemeImgs array when the Gen button is clicked. The property on the chosen image in the array is .url.

We can break this task down into smaller parts.

Firstly, we set the form's onSubmit to equal the name of our new method, which we will call handleSubmit().

We now create the handleSubmit() function above the render() function. We need to preventDefault on the event, otherwise, the method will try to refresh the page.

handleSubmit(event) { event.preventDefault() } 

We also need to bind handleSubmit() in our constructor().

constructor() { super() this.state = { topText: "", bottomText: "", randomImg: "//i.imgflip.com/1bij.jpg", allMemeImgs: [] } this.handleChange = this.handleChange.bind(this) this.handleSubmit = this.handleSubmit.bind(this) } 

Now, we need to get a random number, get the meme from that index and set randomImg to the .url of the random item.

handleSubmit(event) { event.preventDefault() // get a random int (index in the array) // get the meme from that index // set `randomImg` to the `.url` of the random item I grabbed } 

To get a random number, we use Math.floor(Math.random). To make sure that it is one of the indices in our allMemeImgs array, we multiply by the length of the array.

const randNum = Math.floor(Math.random() * this.state.allMemeImgs.length); 

We now set randMemeImg to equal allMemeImgs, with the index of allMemeImgs as the randNum we just got. We then add .url to the end of it.

const randMemeImg = this.state.allMemeImgs[randNum].url; 

Now, all we need to do is update the state by updating the randomImg property with randMemeImg.

this.setState({ randomImg: randMemeImg }); 

Our completed handleSubmit() function looks like this:

handleSubmit(event) { event.preventDefault() const randNum = Math.floor(Math.random() * this.state.allMemeImgs.length) const randMemeImg = this.state.allMemeImgs[randNum].url this.setState({ randomImg: randMemeImg }) } 

Completed Meme Generator

Arbejdsapp

We now have completed the meme generator app, and get a different image every time we hit the Gen button, which is then overlaid with the text we input.

For at fremme vores læring kunne vi lege med kode og se, om vi kan forbedre den eller prøve at få billeder fra en anden API. For nogle virkelig tunge øvelser kunne vi endda slette al koden og prøve at bygge den igen fra bunden.

Tillykke med at have fulgt gennem tutorial og lært alle de færdigheder, der er brugt i dette projekt.

Og hvis du er klar til det, skal du tjekke mit kommende avancerede kursus, da det tager dig til et professionelt niveau i React!