JavaScript React Components Managing State and Data Flow Update State Based on a Player's Index

Rishi B
Rishi B
13,866 Points

how do i get rid of 'Cannot read property 'toString' of undefined' error?

import React, {Component} from 'react';

import Header from './Header';
import Player from './Player';


class App extends Component {

    state = {
        players:[
            {
                name: "Rishi",
                score: 0,
                id: 1
            },
            {
                name: "Guil",
                score: 0,
                id: 2
            } 
        ]
    }   

    handleScoreChange = (index, delta) => {
    //     this.setState( prevState => ({score: prevState.score + 1 }) );
        console.log(index, delta);
     }

    handleRemovePlayer = (id) => {
        this.setState( prevState => {
            return {
                players: prevState.players.filter(p=> p.id!==id)
            }
        })
    }

    render(){
        return(
            <div className="scoreboard">
                <Header title="Scoreboard" totalPlayers={this.state.players.length} />
                {this.state.players.map( (index, player) => 
                    <Player 
                        name = {player.name} 
                        score = {player.score}
                        id = {player.id}
                        index = {index}
                        key = { player.id.toString() }
                        changeScore = {this.handleScoreChange}
                        removePlayer = {this.handleRemovePlayer}
                    />
                )}
            </div>
        )
    }

}

export default App;

2 Answers

Michael Hulet
MOD
Michael Hulet
Treehouse Moderator 47,709 Points

The issue here is that when your render function is called, player.id is undefined. The property player itself might be undefined also. Make sure you're reading a valid value for player from somewhere (such as your component's state), and this error should go away

Rishi B
Rishi B
13,866 Points

It seems that I am reading value from 'players' object from App component state in the above code.. inspite of that, I'm getting error..

Am i wrong??