Question

react js-× TypeError：无法读取未定义的属性“map”

2020-04-01

110

javascript reactjs

我对这段代码有疑问： TypeError：无法读取未定义的属性“map”

请指导我该怎么做

app.js

import React from "react";

import {CardList} from "./componets/card-list/card-list";


class App extends React.Component {
    constructor() {
        super();
        this.state={
            monsters:
                []
        };
    }
    componentDidMount() {
        fetch('http://jsonplaceholder.typicode.com/users')
            .then(res => res.json())
            .then((data) => {
                this.setState({ monsters: data })
            })
    }
    render() {
     return(
         <div>
             <CardList monters={this.state.monsters}/>
         </div>
     )
 }
}
export default App;

和 cardlist.jsx 请指导我该怎么做

import './card-list.css'


export const CardList=(props) => (

     <div className='card-list'>{props.monsters.map(monster =>(<h1 key={monster.id}>{monster.name}</h1>))}

    </div>
);```

Answer 1

您错过了这里：

<CardList monters={this.state.monsters}/>

您将您的道具命名为 monters

Mark Minerov

2020-04-01

Answer 2

您需要将数据的默认值设置为空数组，以防您从获取请求中没有收到任何内容。请尝试以下操作：

import React from "react";

import {CardList} from "./componets/card-list/card-list";


class App extends React.Component {
    constructor() {
        super();
        this.state={
            monsters:
                []
        };
    }
    componentDidMount() {
        fetch('http://jsonplaceholder.typicode.com/users')
            .then(res => res.json())
            .then((data = []) => {
                this.setState({ monsters: data })
            })
    }
    render() {
     return(
         <div>
             <CardList monters={this.state.monsters}/>
         </div>
     )
 }
}
export default App;