TypeError: Cannot read property 'length' of undefined react

Question

我正在用 React 做一个简单的练习。练习的目标是：

从数组中随机抽取水果
记录消息“请给我一个随机水果。”
记录消息“给你：RANDOMFRUIT”
记录消息“美味！我可以再来一份吗？[=39=]
从水果数组中移除水果
记录消息“对不起，我们都出去了。我们还剩下 FRUITSLEFT。

在运行这段代码中，我遇到了以下错误。出于某种原因，"length" 似乎是问题所在。

TypeError: Cannot read property 'length' of undefined
Module../src/index.js
C:/Users/jaina/Desktop/ReactAPPS/exercise1/exercise-one/src/index.js:15
  12 | // Remove the fruit from the array of fruits
  13 | let remaining = remove(foods, fruit);
  14 | // Log the message “I’m sorry, we’re all out. We have FRUITSLEFT left.”
> 15 | console.log(`I’m sorry, we’re all out. We have ${remaining.length} other foods left.`);
  16 |

它还说 __webpack_require__ 以及其他 webpack 警告。但我假设不运行的主要原因是 "length" 未定义。

index.js

import foods from './foods';
import { choice, remove } from './helpers';

// Randomly draw a fruit from the array
let fruit = choice(foods);
// Log the message “I’d like one RANDOMFRUIT, please.”
console.log(`I’d like one ${fruit}, please.`);
// Log the message “Here you go: RANDOMFRUIT”
console.log(`Here you go: ${fruit}`);
// Log the message “Delicious! May I have another?”
console.log('Delicious! May I have another?');
// Remove the fruit from the array of fruits
let remaining = remove(foods, fruit);
// Log the message “I’m sorry, we’re all out. We have FRUITSLEFT left.”
console.log(`I’m sorry, we’re all out. We have ${remaining.length} other foods left.`);

Foods.js

const foods = [
    "", "", "", "", "", "", "", "",
    "", "", "", "", "", "", "",
];

export default foods;

helper.js

function choice(items){
    let idx = Math.floor(Math.random()* items.length);
}

function remove(items, item){
    for (let i = 0; i < items.length; i++){
        if(items[i] === item){
            return [ ...items.slice(0,i), ...items.slice(i+1)];
        }
    }
}

export {choice, remove};

感谢任何帮助。

Answer 1

在helper.js中，如果你的函数remove没有找到任何东西，它将return未定义。然后，当你说...

console.log(`I’m sorry, we’re all out. We have ${remaining.length} other foods left.`);

...您假设 remaining 是一个数组，但它实际上是未定义的。

尝试将 return items; 放在 remove 函数的末尾，在 for 循环之后。

Answer 2

在您上面的代码中，return items 以防在 remove 函数中找不到任何内容。

function remove(items, item){
    for (let i = 0; i < items.length; i++){
        if(items[i] === item){
            return [ ...items.slice(0,i), ...items.slice(i+1)];
        }
    }
    // change this to whatever you want in case it was able to find item to remove
    return items;
}

Answer 3

您的问题似乎出在这里：

function choice(items){
    let idx = Math.floor(Math.random()* items.length);
}

所以let fruit = choice(foods)，fruit永远是未定义的。

尝试 return 辅助函数的值，如下所示：

function choice(items){
   let fruitIndex = Math.floor(Math.random()* items.length);
   return items[fruitIndex];
}

你还应该找到选择的索引和return水果，否则choice将return只有一个数字。

Answer 4

修改您的选择并删除功能

function choice(items) {
    return Math.floor(Math.random()*items.length);
}

function remove(items, item) {
    return items.filter(e => e !== item);
};

TypeError: Cannot read property 'length' of undefined react

TypeError: Cannot read property 'length' of undefined react

javascript

undefined

reactjs

create-react-app