Develop Reference

How to use images in the array in the react?

I am creating a website. I am a beginner. I have an issue. I have an array of react components. I don’t know can I use React components as the array elements. They are images, imported from the folder of my project. Also, I have an array of names of news companies. The idea is to create blocks with the name and image above. I want to create blocks according to the my images array length. So if the length of this array is 4, the cards I have 4. The issue is I can't display images, I imported them to my project. Main code is in the main page component. Also, I have a component called Author Card. In it, I have a React component, that receives name and image as the props and put them in the card Html block.
Here is my main page component code:
import React from 'react';
import AuthorCard from "./MainPageComponents/AuthorCard";
import BBC_Logo from '../assets/images/BBC_Logo.png';
import FOX_Logo from '../assets/images/FOX_Logo.png';
import CNN_Logo from '../assets/images/CNN_logo.png';
import ForbesLogo from '../assets/images/forbes-logo.png';
function MainPage(props) {
const channels = [
{
name: 'BBC',
index: 1
},
{
name: 'FOX',
index: 2
},
{
name: 'CNN',
index: 3
},
{
name: 'FORBES',
index: 4
},
];
const logos = [
<BBC_Logo key={1} />,
<FOX_Logo key={2}/>,
<CNN_Logo key={3}/>,
<ForbesLogo key={4}/>
];
return (
<div className="main-page">
<div className="main-page_container">
<section className="main-page_channels">
{channels.map( (channel) => {
logos.map( (logo) => {
return <AuthorCard name={channel.name} img={logo} />
})
})}
</section>
</div>
</div>
);
}
export default MainPage;
Here is my Author Card component code:
import React from 'react';
function AuthorCard(props) {
return (
<div className="author-card">
<div className="author-img">
{props.img}
</div>
<div className="author-name">
{props.name}
</div>
</div>
);
}
export default AuthorCard;
Please, help!

I would handle this a bit differently. First thing the way you import your logos is not imported as a component. Rather you get the path/src of the image which you can then use in a component. Read more about that here: https://create-react-app.dev/docs/adding-images-fonts-and-files/
So the way I would do this is to put the logo img src into your channels array and then pass that img src to the AuthorCard component. Then in the AuthorCard component your use a component to render the image. Like this:
import React from "react";
import BBC_Logo from "../assets/images/BBC_Logo.png";
import FOX_Logo from "../assets/images/FOX_Logo.png";
import CNN_Logo from "../assets/images/CNN_logo.png";
import ForbesLogo from "../assets/images/forbes-logo.png";
export default function App() {
return (
<div className="App">
<MainPage />
</div>
);
}
const channels = [
{
name: "BBC",
index: 1,
img: BBC_Logo
},
{
name: "FOX",
index: 2,
img: FOX_Logo
},
{
name: "CNN",
index: 3,
img: CNN_Logo
},
{
name: "FORBES",
index: 4,
img: ForbesLogo
}
];
function MainPage(props) {
return (
<div className="main-page">
<div className="main-page_container">
<section className="main-page_channels">
{channels.map((channel) => {
return <AuthorCard name={channel.name} img={channel.img} />;
})}
</section>
</div>
</div>
);
}
function AuthorCard(props) {
return (
<div className="author-card">
<div className="author-img">
<img src={props.img} alt="author card" />
</div>
<div className="author-name">{props.name}</div>
</div>
);
}

Here, we are using the map function to iterate over the channels array and render an AuthorCard component for each channel. We pass the name property to the AuthorCard component, as well as the corresponding logo from the logos array.
Note that we are also passing a key prop to the AuthorCard component to help React identify each component uniquely. In this case, we're using the index property of each channel object.

How to .Map over different props that are passed into a component?

I'm new to React but hopefully someone can help!
So I've just created a component that takes in a value (via prop) and then .maps over that value creating an Image slider. The props are all an array of objects that contain different values such as :
const Songs = [
{
artist: 'Artist Name',
song: 'Song Name',
lenght: '2:36',
poster: 'images/....jpg'
},
{
artist: 'Artist Name',
song: 'Song Name',
lenght: '2:36',
poster: 'images/....jpg'
},
]
I have been making the same component over and over again because I don't know how to make the 'prop'.map value dynamic. Essentially I don't know how to change the value before the .map each different prop.
Here's an example. I want to make 'Songs'.map dynamic so the new props can replace that so they can also be mapped. Maybe there's another way. Hopefully some can help.
import React from 'react';
import { FaCaretDown } from 'react-icons/fa';
function ImageSlider({Songs, KidsMovies, Movies, TvShows}) {
return (
<>
{Songs.map((image, index) => (
<div className="movie-card">
<img src={'https://image.tmdb.org/t/p/w500' + image.poster_path}
className='movie-img' />
<h5 className='movie-card-desc'>{image.original_title}</h5>
<p className='movie-card-overview'>{movie.overview}</p>
</div>
))}
</>
);
}
export default ImageSlider;

Given your example,
I feel like all you need is render ImageSlides for each array
function ImageSlider({ items }) {
return (
<>
{items.map((item, idx) => (
<div ... key={idx}> // be careful to not forget to put a key when you map components
...
</div>
))}
</>
);
}
When rendering your component
function OtherComponent({ songs, kidsMovies, movies, tvShows }) {
return (
<div>
<ImageSlider items={songs} />
<ImageSlider items={kidsMovies} />
<ImageSlider items={movies} />
<ImageSlider items={tvShows} />
</div>
);
}

Property 'map' of undefined in React

I'm learning a react course online. When I try to display the list of items from an array using map to display in a child component , I keep getting "cannot read property map of undefined.
Error is thrown while fetching data from users
import React, { Component } from "react";
import ReactDOM from "react-dom";
let userList = [
{ name: "John", age: 24, place: "India" },
{ name: "Henry", age: 24, place: "India" },
{ name: "Ulrich", age: 24, place: "India" }
];
const AppChild = ({ name, age, place, Graduated }) => {
return (
<section>
<p>name: {name}</p>
<p>age: {age}</p>
<p>place: {place}</p>
{/* access the value via props */}
<p>Graduated: {Graduated ? "yes!" : "no!"}</p>
</section>
);
};
export default class App extends Component {
state = {
userExists: true,
isGraduated: true,
loading: true,
};
toggleStatus = () => {
this.setState(prevState => ({
userExists: !prevState.userExists // value : false
}));
};
render() {
const { users } = this.props;
return (
<div>
<h2>Profile</h2>
<h4>
Profile Status is {this.state.userExists ? "Updated" : "Outdated"}
<br />
<button onClick={this.toggleStatus}>Check Status</button>
</h4>
{users.map(user => (
<AppChild
name={user.name}
age={user.age}
place={user.place}
Graduated={this.state.isGraduated} // passing state to child component
/>
))}
</div>
);
}
}
ReactDOM.render(<App users={userList} />, document.getElementById("root"));

To figure out the problem, we follow the bouncing ball. From the error message, I guess that the problem occurs on the line
{users.map(user => (
(You can confirm this from the stack trace given with the error message.)
The error tells you that users is undefined. So we look at the declaration for users:
const { users } = this.props;
Ok, so it is really this.props.users. So we look where this is passed in:
ReactDOM.render(<App users={userList} />, document.getElementById("root"));
Here you are passing the value of userList to a prop named users. However, in the code you show here, there is no variable named userList. This is as far as we can go with the information you have given. You need to find where this variable is declared and initialized to continue solving the problem.

Below is the correct code. In the previous code I was trying to render <App/> in both index.js and App.js. Thanks everyone for helping me out
=>index.js
import React from "react"
import ReactDOM from "react-dom"
import App from "./App"
let userList = [
{ name: "John", age: 24, place: "India" },
{ name: "Henry", age: 24, place: "India" },
{ name: "Ulrich", age: 24, place: "India" }
];
ReactDOM.render(<App users={userList} />, document.getElementById("root"));
=> App.js
import React, { Component } from "react";
// child component
const AppChild = ({ name, age, place, Graduated }) => {
return (
<section>
<p>name: {name}</p>
<p>age: {age}</p>
<p>place: {place}</p>
{/* access the value via props */}
<p>Graduated: {Graduated ? "yes!" : "no!"}</p>
</section>
);
};
// parent component
export default class App extends Component {
state = {
userExists: true,
isGraduated: true,
loading: true,
};
toggleStatus = () => {
this.setState(prevState => ({
userExists: !prevState.userExists // value : false
}));
};
render() {
const { users } = this.props;
return (
<div>
<h2>Profile</h2>
<h4>
Profile Status is {this.state.userExists ? "Updated" : "Outdated"}
<br />
<button onClick={this.toggleStatus}>Check Status</button>
</h4>
{users.map((user) => {
return(
<AppChild
name={user.name}
age={user.age}
place={user.place}
Graduated={this.state.isGraduated} // passing state to child component
/>
)})}
</div>
);
}
}

If you try to log users after following line of code
const { users } = this.props;
you'll see users is undefined.
Error message "cannot read property map of undefined" says the same thing, you can not apply map helper on an undefined variable. The map works with arrays

Moving elements onclick from one array to another. Content in new array objects empty / not copied?

Good evening,
as a learning project I want to build a simple "Learning Cards" App. The structure is quite simple: you have cards with questions. After a button click, you can show the correct solution. You can also click on "Question solved" to move the learning card to the absolved cards.
I am struggling to realize the "moving the learning card to the absolved" cards part. I have a "questions" array. After "onSolvedClick" the solved card gets copied to the "solved" array which is set as the new solved state.
When I click on the "Frage gelöst" (question solved) button, a new card appears in the solved questions region. The problem is: the new card is empty (without the question / answer). It would be great if someone could help me at this point! I already spent hours on this problem today.
I guess my mistake is within the App.Js code, probably in "onSolvedKlick" or "solveFragen".
Thanks a lot!
App.Js:
import React, {Component} from 'react';
import CardList from './CardList.js';
import { fragen } from './fragen';
import SearchBox from './SearchBox';
class App extends Component { // As Class to access objects
constructor () {
super();
this.state = { // State needed to change state
fragen: fragen,
solved : [] ,
searchfield: ''
}
}
onSearchChange = (event) => {
this.setState({searchfield: event.target.value});
}
onSolvedKlick = (id) => {
console.log("Klick on solved"+id);
var frage = this.state.fragen.filter(function(e) // Bei Klick auf Solved: filtere aus Ursprungsarray das Element mit gelöster iD
{
return e.id === id;
});
console.log(frage);
const newSolvedArray = this.state.solved.slice();
newSolvedArray.push(frage);
this.setState({solved: newSolvedArray});
}
render(){ // DOM rendering
const filteredFragen = this.state.fragen.filter(fragen =>{
return fragen.frage.toLowerCase().includes(this.state.searchfield.toLowerCase());
})
const solveFragen = this.state.solved;
return(
<div className='tc'>
<h1>Learning Cards</h1>
<SearchBox searchChange={this.onSearchChange}/>
<h2>Cards: To be learned!</h2>
<div>
<CardList fragen={filteredFragen} onSolvedKlick={this.onSolvedKlick}/>
<CardList fragen={solveFragen} onSolvedKlick={this.onSolvedKlick}/>
</div>
</div>
)
}
}
export default App;
CardList.js:
import React from 'react';
import Card from './Card';
const CardList = ({fragen, onSolvedKlick}) => {
const cardComponent = fragen.map( (user, i) => {
return(<Card key={i} id={fragen[i].id} frage = {fragen[i].frage} antwort = { fragen[i].antwort} onSolvedKlick = {onSolvedKlick}/>);
}
)
return (
<div>
{cardComponent}
</div>
);
}
export default CardList;
Card.js:
import React, {Component} from 'react';
import 'tachyons';
class Card extends Component {
constructor(props) {
super(props);
this.state = {
frage : props.frage,
showAnswer : false
};
}
_showAnswer = () => {
const before = this.state.showAnswer;
const after = !before;
this.setState({
showAnswer: after
});
}
render() {
return (
<div className ="fl w-50 w-25-m w-20-l pa2 bg-light-red ma3">
<div>
<h2>{this.props.frage}</h2>
{ this.state.showAnswer && (<div>{this.props.antwort}</div>) }
<p></p>
<input type="button" value="Antwort anzeigen" className ="ma2"
onClick={this._showAnswer.bind(null)}
/>
<input type="button" name="solved" value="Frage gelöst" className = "ma2 bg-light-green"
onClick={() =>this.props.onSolvedKlick(this.props.id)}
/>
</div>
</div>
);
}
}
fragen.js (Questions):
export const fragen = [
{
id: 1,
frage: 'What are trends in CPU design?',
antwort: 'Multi-core processors, SIMD support, Combination of core private and shared caches Heterogeneity, Hardware support for energy control',
topic: 'Cloud'
},
{
id: 2,
frage: 'What is typical for multi-core processors?',
antwort: 'Cache Architecture (L1 private to core, L2 private to tile), Cache Coherence',
topic: 'Cloud'
},
{
id: 3,
frage: 'What memory modes exist?',
antwort: 'Flat mode, Cache Mode, Hybrid Mode',
topic: 'Cloud'
},
{
id: 4,
frage: 'What memory modes exist?',
antwort: 'Flat mode, Cache Mode, Hybrid Mode',
topic: 'Cloud'
},
];

Try this on your onSolvedKlick function:
onSolvedKlick = (id) => {
console.log("Klick on solved"+id);
var frage = this.state.fragen.filter((e) => e.id === id);
this.setState({solved: [...this.state.solved, frage]});
}
Try to avoid so many empty lines.
Also keep your code always in english so it's easier for others to understand. I had the luck to be german too :)

Assuming that you want to move the questions from fragen array to solved array, here is how to do that.
onSolvedKlick = id => {
console.log("Klick on solved" + id);
var elementPos = this.state.fragen.map(function(x) {return x.id; }).indexOf(id); // Find the position of the selected item in the fragen
const currentItem = this.state.fragen.splice(elementPos,1)
const newSolvedArray = this.state.solved;
newSolvedArray.push(currentItem[0]);//splice gives an array
this.setState({ solved: newSolvedArray }, function() {console.log(this.state)});
};

How to render a text preview from a collection field in Meteor + React?

I'm trying to show a text preview for a list of posts. I have a list of posts that are rendered in the home blog page, each post only shows title, author and an anchor tag as a link to a view that shows a single post with all the data that contains the selected post. Now in the home blog page I need to show a text preview of the post in addition to title and author but I don't have any idea of how to grab a part of the post content and show it as a preview.
I'm a beginner with Meteor and React. If someone could give me some advise, it would be great. Here is the code:
Collections.jsx
export const Posts = new Mongo.Collection('Posts');
export const PostSchema = Astro.Class({
name: 'PostSchema',
collection: Posts,
fields: {
title: {
validator: Validators.and([
// more validators...
]),
},
content: { // I need to show a preview of this content
validator : Validators.and([
Validators.required(),
Validators.string(),
Validators.minLength(3)
])
},
author: {
validator: Validators.and([
// more validators
])
},
category: {
validator: Validators.and([
// more validators
])
},
tags: {
validator: Validators.and([
// more validators
])
},
}
});
Here is where I show the posts list.
Blog.jsx
// other imports
import { Posts } from '../../lib/collections.jsx';
class Blog extends Component {
render() {
let content = (
<div>
<h1>Posts</h1>
{this.props.posts.map((post, idx) => (
<Post key={idx} post={post} />
))}
</div>);
if (!this.props.ready) {
content = <p>LOADING...</p>;
}
return content;
}
}
Blog.propTypes = {
ready: React.PropTypes.bool.isRequired,
posts: React.PropTypes.array.isRequired,
};
export default createContainer((params) => {
const handle = Meteor.subscribe('posts');
let posts = Posts.find({}, { sort: { createdAt: -1 } }).fetch();
if (params.category) {
posts = Posts.find({ category: params.category },
{ sort: { createdAt: -1 } }).fetch();
}
return {
ready: handle.ready(),
posts,
};
}, Blog);
/**
* POST
* Here is where I don't know how to show the text preview
*/
const Post = (props) => {
const {
title,
author,
slug,
category,
content,
} = props.post;
return (
<div>
<article className="new-resolution">
<p>Title:{title}</p>
<p>Author:{author}</p>
<p>{content}</p>
<a href={`/blog/kategorie/${category}/${slug}`}>
Weiter lesen...
</a>
</article>
</div>
);
};
Post.propTypes = {
post: PropTypes.object.isRequired,
};

Since I din't have to much time to resolve this in a much fancy way, I just decide to add a new field in my collection named "preview". In the form post I added a new text area with a limit of characters and this would be displayed in the Post.jsx <p>Preview:{preview}</p>.