Ytukyg

I'm trying to create a counter for each item in a list in React. I want each to be incremented or decremented individually depending on what the user clicks on. This issue is that all counters increment and decrement on click
of a single element, but I would like only the clicked element's counter to change.

this is my code:

class name extends Component {



    constructor(){

        super()



        this.state = {

          news: ,

          voteing: 0

        }

    }



    onVoting(type){

        this.setState(prevState => {

           return {voteing: type == 'add' ? prevState.voteing + 1: prevState.voteing- 1}

        });

    }



    render() {

      return (

        <React.Fragment>

          <Content>

            {

              this.state.news.map((item, i)=>{

                return (

                <Item key={i}>

                  <text>

                    {item.subject}

                    {item.details}

                  </text>

                  <Votering>

                    <img src="" onClick={this.onVoting.bind(this, 'add')} />

                    <div value={this.state.voteing}>{this.state.voteing}</div>

                    <img src="" onClick={this.onVoting.bind(this, 'min')} />

                 </Votering>

                </Item>

                )

              })

            }

          </Content>

        </React.Fragment>

      )

    }

  }

I'm trying to do this:

<img src="" onClick={this.onVote(i).bind(this, 'add')} />

but it doesn't work also tried this.onVote(item.i) and same result

The reason all your items' counts change when any of them is clicked on is that they all share the same vote count value, voteing in the name component's state.

To fix this, you should break each item into its own stateful component. So that each can track its own click count.

For example:

class name extends Component {

    constructor(){

        super();

        this.state = {

          news: 

        }

    }



    render() {

      return (

        <React.Fragment>

          <Content>

            {

              this.state.news.map((item, i) => {

                return <NewsItem key={ i }

                           subject={ item.subject }

                           details={ item.details }

                       />

              })

            }

          </Content>

        </React.Fragment>

      )

    }

  }



class NewsItem extends Component {

    constructor() {

        super();

        this.state = {

            voteCount = 0

        }

    }



    handleVote(type) {

        this.setState(prevState => ({

            voteCount: type === "add" ? prevState.voteCount + 1 : prevState.voteCount - 1

        }));

    }



    render() {

        const { subject, details } = this.props;

        const { voteCount } = this.state;



        return (

            <Item>

              <text>

                { subject }

                { details }

              </text>

              <Votering>

                <img src="" onClick={ this.handleVote.bind(this, 'add') } />

                <div value={ voteCount }>{ voteCount }</div>

                <img src="" onClick={ this.handleVote.bind(this, 'min') } />

             </Votering>

            </Item>

        )

    }

}

You could also maintain separate counts for each item within the parent component, but I find breaking into separate components to be much cleaner.

I cannot really see how you would like to see voting as part of the local component state, as it really has to do (in my opinion), with the entities on which you can vote.

So if I were you, I would rewrite the code slightly different. As I do not know what you intend to do afterwards with the votes (this rather assumes like a live process, or at least a kind of save button, as it is saved here in the local VotingApp state), I just save everything to the local state, how you would handle that is not really my intend to answer.

So personally, I would rather go for one functional component, just rendering the news item and it's voting capability, where the voteCount is part of the item entity. If this is not how you receive the data, nothing stops you from adding the data after your fetch and before really showing it on the screen. The app itself will receive the changes and the item that will be changed, and what it does there-after, would be all up to you ;)

const { Component } = React;



const NewsItem = ( item ) => {

  const { subject, details, voteCount, handleVoteChange } = item;

  return (

    <div className="news-item">

      <div className="news-vote">

        <div className="vote-up" title="Vote up" onClick={ () => handleVoteChange( item, 1 ) }></div>

        <div className="vote-count">{ voteCount }</div>

        <div className="vote-down" title="Vote down" onClick={ () => handleVoteChange( item, -1 ) }></div>

      </div>

      <div className="news-content">

        <h3>{ subject }</h3>

        <div>{ details }</div>

      </div>

    </div>

  );

};



class VotingApp extends Component {

  constructor( props ) {

    super();

    this.handleVoteChange = this.handleVoteChange.bind( this );

    // by lack of fetching I add the initial newsItems to the state

    // and work by updating local state on voteChanges

    // depending on your state management (I guess you want to do something with the votes)

    // you could change this

    this.state = {

      newsItems: props.newsItems

    };

  }

  handleVoteChange( item, increment ) {

    this.setState( ( prevState ) => {

      const { newsItems } = prevState;

      // updates only the single item that has changed

      return { 

        newsItems: newsItems

          .map( oldItem => oldItem.id === item.id ? 

            { ...oldItem, voteCount: oldItem.voteCount + increment } : 

            oldItem ) };

    } );

  }

  render() {

    const { newsItems =  } = this.state;

    return (

      <div className="kiosk">

        { newsItems.map( item => <NewsItem 

            key={ item.id } 

            {...item} 

            handleVoteChange={this.handleVoteChange} /> ) }

      </div>

    );

  }

}



// some bogus news items

const newsItems = [

  { id: 1, voteCount: 0, subject: 'Mars in 2020', details: 'Tesla will send manned BFR rockets to Mars in 2020' },

  { id: 2, voteCount: -3, subject: 'Stackoverflow rocks', details: 'Stackoverflow is booming thanks to the new friendly policy' },

  { id: 3, voteCount: 10, subject: 'DS9: Healthy living', details: 'Eat rice everyday and drink only water, and live 10 years longer, says Dax to Sisko, Sisko suprises her by saying that like that, he doesn't want to live 10 years longer...' }

];



// render towards the container

const target = document.querySelector('#container');

ReactDOM.render( <VotingApp newsItems={ newsItems } />, target );

.kiosk {

  display: flex;

  flex-wrap: no-wrap;

}

.news-item {

  display: flex;

  justify-content: flex-start;

  width: 100%;

}

.news-vote {

  display: flex;

  flex-direction: column;

  align-items: center;

  padding-left: 10px;

  padding-right: 10px;

}

.news-vote > * {

  cursor: pointer;

}

.news-content {

  display: flex;

  flex-direction: column;

}

.vote-up::before {

  content: '▲';

}

.vote-down::before {

  content: '▼';

}

.vote-up:hover, .vote-down:hover {

  color: #cfcfcf;

}

h3 { margin: 0; }

<script id="react" src="https://cdnjs.cloudflare.com/ajax/libs/react/15.6.2/react.js"></script>

<script id="react-dom" src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/15.6.2/react-dom.js"></script>

<script id="prop-types" src="https://cdnjs.cloudflare.com/ajax/libs/prop-types/15.6.0/prop-types.js"></script>

<script id="classnames" src="https://cdnjs.cloudflare.com/ajax/libs/classnames/2.2.5/index.js"></script>

<div id="container"></div>

A few things I noticed unrelated to your question.

1) onVoting should be bound in your constructor or use onVoting = () => { ..... }

2) in your render function you have onVote instead of onVoting

On to your main question, in your state you are only maintaining one counter that is displayed and changed for all news elements. an easy way to get around this is to create a new react element for each news article that will handle the voting for each article.

class parent extends Component {



constructor(){

    super()



    this.state = {

      news: null,

    }

}

componentDidMount() {

 // fetch data from api and minipulate as needed

 this.setState({news: dataFromApi})

}



render() {

  return (

      <Content>

        {

          this.state.news.map((item, i)=>{

            return (

            <NewChildComponent data={item}/>

            )

          })

        }

      </Content>

  )

}

}



class NewChildComponent extends Component {

    constructor() {

        super()

        this.state = {

             voting: 0,

        }

    }

    onVoting = (e) => {

       this.setState(prevState => ({

        voteCount: e.target.name === "add" ? prevState.voteCount + 1 : prevState.voteCount - 1

       }));

    }

    render () {

         const {data} = this.props;

         return (

            <Item key={data.uniqueID}>

              <text>

                {data.subject}

                {data.details}

              </text>

              <Votering>

                <img src="" onClick={this.onVoting} name="add"/>

                <div value={this.state.voteing}>{this.state.voteing}</div>

                <img src="" onClick={this.onVoting} name="min"/>

             </Votering>

            </Item>

           )

    }

}

A little background on why you should not bind in your render function. https://medium.freecodecamp.org/why-arrow-functions-and-bind-in-reacts-render-are-problematic-f1c08b060e36

Here’s why: The parent component is passing down an arrow function on
props. Arrow functions are reallocated on every render (same story
with using bind). So although I’ve declared User.js as a
PureComponent, the arrow function in User’s parent causes the User
component to see a new function being sent in on props for all users.
So every user re-renders when any delete button is clicked. 👎

Also why you should not use an index as a key in React.
https://reactjs.org/docs/lists-and-keys.html

We don’t recommend using indexes for keys if the order of items may
change. This can negatively impact performance and may cause issues
with component state. Check out Robin Pokorny’s article for an
in-depth explanation on the negative impacts of using an index as a
key. If you choose not to assign an explicit key to list items then
React will default to using indexes as keys.

Here is an in-depth explanation about why keys are necessary if you’re
interested in learning more.