JSX不渲染

Question

I'm working through an online course on React and Meteor. Whenever I hit the submit button it registers the new player in the database, but it doesn't actually show p on the client side. I get the following in the console:

Exception from Tracker recompute function: Invariant Violation: Objects are not valid as a React child (found: object with keys {playerName}). If you meant to render a collection of children, use an array instead or wrap the object using createFragment(object) from the React add-ons."

 import React from 'react';
 import ReactDOM from 'react-dom';
 import {Meteor} from 'meteor/meteor';
 import {Tracker} from 'meteor/tracker';

 import {Players} from './../imports/api/players.js';

 const renderPlayers = (playersList) => {

    return playersList.map( (player) =>{
        return <p key={player._id}>{player.name} has {player.score} points!</p>;
    });
 };

const handleSubmit = (e) => {
    let playerName = e.target.playerName.value;

    e.preventDefault();

    if (playerName) {

    e.target.playerName.value = '';

    Players.insert({
    name: playerName,
    score: 0
    });
   }
 };
 Meteor.startup( () => {

    Tracker.autorun( () => {
        let players = Players.find().fetch();
        let title = 'Score Keeper';
        let name = 'Bill';
        let jsx = (
            <div>
                <h1>{title}</h1>
                <p>Hello {name}!</p>
                <p>Second p</p>
                {renderPlayers(players)}
                <form onSubmit={handleSubmit}>
                    <input type="text" name="playerName" placeholder="Player Name"/>
                    <button>Add Player</button>
                </form>
            </div>
            );
        ReactDOM.render(jsx, document.getElementById('app'));
    });
});

Answer 1

I'm almost positive that this line:
let players = Players.find().fetch(); is not returning an array as you expected.
I'm guessing .fetch is returning an object (maybe with .data in it?) and that's why you are getting this error.
Try logging the players object after .fetch finished and see what's inside this object.