How to fix 'TypeError: Cannot read property 'map' of undefined' in React

Question

你好，我是 React 的新手，我试图显示我在 state 中创建的名为 Todo 的数组，但是我收到错误 "TypeError: Cannot read property 'map' of undefined"。你能告诉我哪里做错了吗？

这是我的代码

index.js

import React from 'react';
import ReactDOM from 'react-dom';

import App from './App';
import * as serviceWorker from './serviceWorker';

ReactDOM.render(<App />, document.getElementById('root'));

serviceWorker.unregister();

App.js

import React, { Component } from 'react';
import Todos from './component/Todos.js';
import './App.css'

class App extends Component {
  state={
    todos:[
        {
            id: 1,
            title:'Star Wars',
            point:9,
            watched: true
        },
        {
            id: 2,
            title:'Into the Wild',
            point:null,
            watched: false
        },
        {
            id: 3,
            title:'Enter the Void',
            point:6,
            watched: true
        },
        {
            id: 4,
            title:'Tschick',
            point:7.5,
            watched: true
        }
    ]
  }
  render() {
    return (
      <div className="App">
       <Todos />
      </div>
    );
  }
}

export default App;

Todo.js

import React, { Component } from 'react';


class Todos extends Component {

  render() {

    return this.props.todos.map((todo) => (
        <div>
        <h3>{todo.title}</h3>
        </div>
    ));
  }
}


export default Todos;

The error that I get

Answer 1

您没有将 todos 变量传递给您的组件。

您必须像这样传入属性：

<Todos todos={this.state.todos} />

Answer 2

在您的 App.js 中从状态调用待办事项

<Todos todos={this.state.todos}/>

之后它应该可以正常工作

How to fix 'TypeError: Cannot read property 'map' of undefined' in React

How to fix 'TypeError: Cannot read property 'map' of undefined' in React

reactjs

map-function