javascript - 类型错误 : Cannot read property 'map' of undefined | ReactJS

Question

我收到错误TypeError:无法读取未定义的属性“map”。我只是遵循 YouTube 上的 freeCodeCamps 指南，名为“React 教程:使用 React 和 Netlify 从头开始​​构建电子商务网站”。我正在复制所有代码，以便它们是相同的。我想知道是什么原因导致了这个问题。

import React, { Component } from "react";
import Product from "./Product";
import Title from "./Title";
import { storeProducts } from "../data";
import { ProductConsumer } from "../context";

class ProductList extends Component {
  state = {
    products: storeProducts
  };
  render() {
    return (
      <React.Fragment>
        <div className="py-5">
          <div className="container">
            <Title name="our" title="products" />

            <div className="row">
              <ProductConsumer>
                {value => {
                  return value.products.map(product => {
                    return <Product key={product.id} product={product} />;
                  });
                }}
              </ProductConsumer>
            </div>
          </div>
        </div>
      </React.Fragment>
    );
  }
}

export default ProductList;

这是其余文件:

context.js

import React, { Component } from "react";
import { storeProducts, detailProduct } from "./data";

const ProductContext = React.createContext();
//Provider
//Consumer

class ProductProvider extends Component {
  state = {
    products: storeProducts,
    detailProduct: detailProduct
  };
  handleDetail = () => {
    console.log("hello from detail");
  };
  addToCart = () => {
    console.log("hello from addToCart");
  };
  render() {
    return (
      <ProductContext.Provider
        value={{
          ...this.state,
          handleDetail: this.handleDetail,
          addToCart: this.addToCart
        }}
      >
        {this.props.children}
      </ProductContext.Provider>
    );
  }
}

const ProductConsumer = ProductContext.Consumer;

export { ProductProvider, ProductConsumer };

product.js

import React, { Component } from "react";

class Product extends Component {
  render() {
    return (
      <div>
        <h3>This is a product</h3>
      </div>
    );
  }
}

export default Product;

data.js

/* 
https://www.iconfinder.com/icons/1243689/call_phone_icon
Creative Commons (Attribution 3.0 Unported);
https://www.iconfinder.com/Makoto_msk */

export const storeProducts = [
  {
    id: 1,
    title: "Google Pixel - Black",
    img: "img/product-1.png",
    price: 10,
    company: "GOOGLE",
    info:
      "Lorem ipsum dolor amet offal butcher quinoa sustainable gastropub, echo park actually green juice sriracha paleo. Brooklyn sriracha semiotics, DIY coloring book mixtape craft beer sartorial hella blue bottle. Tote bag wolf authentic try-hard put a bird on it mumblecore. Unicorn lumbersexual master cleanse blog hella VHS, vaporware sartorial church-key cardigan single-origin coffee lo-fi organic asymmetrical. Taxidermy semiotics celiac stumptown scenester normcore, ethical helvetica photo booth gentrify.",
    inCart: false,
    count: 0,
    total: 0
  },
  {
    id: 2,
    title: "Samsung S7",
    img: "img/product-2.png",
    price: 16,
    company: "SAMSUNG",
    info:
      "Lorem ipsum dolor amet offal butcher quinoa sustainable gastropub, echo park actually green juice sriracha paleo. Brooklyn sriracha semiotics, DIY coloring book mixtape craft beer sartorial hella blue bottle. Tote bag wolf authentic try-hard put a bird on it mumblecore. Unicorn lumbersexual master cleanse blog hella VHS, vaporware sartorial church-key cardigan single-origin coffee lo-fi organic asymmetrical. Taxidermy semiotics celiac stumptown scenester normcore, ethical helvetica photo booth gentrify.",
    inCart: false,
    count: 0,
    total: 0
  },
  {
    id: 3,
    title: "HTC 10 - Black",
    img: "img/product-3.png",
    price: 8,
    company: "htc",
    info:
      "Lorem ipsum dolor amet offal butcher quinoa sustainable gastropub, echo park actually green juice sriracha paleo. Brooklyn sriracha semiotics, DIY coloring book mixtape craft beer sartorial hella blue bottle. Tote bag wolf authentic try-hard put a bird on it mumblecore. Unicorn lumbersexual master cleanse blog hella VHS, vaporware sartorial church-key cardigan single-origin coffee lo-fi organic asymmetrical. Taxidermy semiotics celiac stumptown scenester normcore, ethical helvetica photo booth gentrify.",
    inCart: false,
    count: 0,
    total: 0
  },
  {
    id: 4,
    title: "HTC 10 - White",
    img: "img/product-4.png",
    price: 18,
    company: "htc",
    info:
      "Lorem ipsum dolor amet offal butcher quinoa sustainable gastropub, echo park actually green juice sriracha paleo. Brooklyn sriracha semiotics, DIY coloring book mixtape craft beer sartorial hella blue bottle. Tote bag wolf authentic try-hard put a bird on it mumblecore. Unicorn lumbersexual master cleanse blog hella VHS, vaporware sartorial church-key cardigan single-origin coffee lo-fi organic asymmetrical. Taxidermy semiotics celiac stumptown scenester normcore, ethical helvetica photo booth gentrify.",
    inCart: false,
    count: 0,
    total: 0
  },
  {
    id: 5,
    title: "HTC Desire 626s",
    img: "img/product-5.png",
    price: 24,
    company: "htc",
    info:
      "Lorem ipsum dolor amet offal butcher quinoa sustainable gastropub, echo park actually green juice sriracha paleo. Brooklyn sriracha semiotics, DIY coloring book mixtape craft beer sartorial hella blue bottle. Tote bag wolf authentic try-hard put a bird on it mumblecore. Unicorn lumbersexual master cleanse blog hella VHS, vaporware sartorial church-key cardigan single-origin coffee lo-fi organic asymmetrical. Taxidermy semiotics celiac stumptown scenester normcore, ethical helvetica photo booth gentrify.",
    inCart: false,
    count: 0,
    total: 0
  },
  {
    id: 6,
    title: "Vintage Iphone",
    img: "img/product-6.png",
    price: 17,
    company: "apple",
    info:
      "Lorem ipsum dolor amet offal butcher quinoa sustainable gastropub, echo park actually green juice sriracha paleo. Brooklyn sriracha semiotics, DIY coloring book mixtape craft beer sartorial hella blue bottle. Tote bag wolf authentic try-hard put a bird on it mumblecore. Unicorn lumbersexual master cleanse blog hella VHS, vaporware sartorial church-key cardigan single-origin coffee lo-fi organic asymmetrical. Taxidermy semiotics celiac stumptown scenester normcore, ethical helvetica photo booth gentrify.",
    inCart: false,
    count: 0,
    total: 0
  },
  {
    id: 7,
    title: "Iphone 7",
    img: "img/product-7.png",
    price: 30,
    company: "apple",
    info:
      "Lorem ipsum dolor amet offal butcher quinoa sustainable gastropub, echo park actually green juice sriracha paleo. Brooklyn sriracha semiotics, DIY coloring book mixtape craft beer sartorial hella blue bottle. Tote bag wolf authentic try-hard put a bird on it mumblecore. Unicorn lumbersexual master cleanse blog hella VHS, vaporware sartorial church-key cardigan single-origin coffee lo-fi organic asymmetrical. Taxidermy semiotics celiac stumptown scenester normcore, ethical helvetica photo booth gentrify.",
    inCart: false,
    count: 0,
    total: 0
  },
  {
    id: 8,
    title: "Smashed Iphone",
    img: "img/product-8.png",
    price: 2,
    company: "apple",
    info:
      "Lorem ipsum dolor amet offal butcher quinoa sustainable gastropub, echo park actually green juice sriracha paleo. Brooklyn sriracha semiotics, DIY coloring book mixtape craft beer sartorial hella blue bottle. Tote bag wolf authentic try-hard put a bird on it mumblecore. Unicorn lumbersexual master cleanse blog hella VHS, vaporware sartorial church-key cardigan single-origin coffee lo-fi organic asymmetrical. Taxidermy semiotics celiac stumptown scenester normcore, ethical helvetica photo booth gentrify.",
    inCart: false,
    count: 0,
    total: 0
  }
];

export const detailProduct = {
  id: 1,
  title: "Google Pixel - Black",
  img: "img/product-1.png",
  price: 10,
  company: "google",
  info:
    "Lorem ipsum dolor amet offal butcher quinoa sustainable gastropub, echo park actually green juice sriracha paleo. Brooklyn sriracha semiotics, DIY coloring book mixtape craft beer sartorial hella blue bottle. Tote bag wolf authentic try-hard put a bird on it mumblecore. Unicorn lumbersexual master cleanse blog hella VHS, vaporware sartorial church-key cardigan single-origin coffee lo-fi organic asymmetrical. Taxidermy semiotics celiac stumptown scenester normcore, ethical helvetica photo booth gentrify.",
  inCart: false,
  count: 0,
  total: 0
};

Answer 1

value 未定义，因为尚未调用 ProductProvider 组件来创建 ProductContext.Provider。

您可以通过在主文件中导入 ProductProvider 来替换 React.Fragment 来实现此目的。