如何使用 React 访问嵌套的 JSON 对象数据？

Question

I am working on project where I want to display results to user, but I am stuck when rendering JSON object data; it gives an error state:

'map' is not a function

App.js

import React, { useState, useEffect } from "react";
import "./App.css";
import { api } from "./data";

const App = () => {
  const [state, setState] = useState([]);
  useEffect(() => {
    setState(api);
    //console.log(state)
  }, [state]);

  const maping = () => {
    state.map((item, index) => (
      <h3 key={index}>{item}</h3>
    ))
  }

  return (
    <div className="App">
      <h3> json data rendering test</h3>
      {maping()}
    </div>
  );
};
export default App;

And here is my json data

export const api = {
  success: true,
  count: 4,
  pagination: {},
  data: [
    {
      location: {
        type: "Point",
        coordinates: [-71.525909, 41.483657],
        formattedAddress: "45 Upper College Rd, Kingston, RI 02881-2003, US",
        street: "45 Upper College Rd",
        city: "Kingston",
        state: "RI",
        zipcode: "02881-2003",
        country: "US"
      },
      careers: [
        "Mobile Development",
        "Web Development",
        "Data Science",
        "Business"
      ],
      photo: "no-photo.jpg",
      housing: false,
      jobAssistance: true,
      jobGuarantee: true,
      acceptGi: true,
      _id: "5d725a1b7b292f5f8ceff788",
      user: "5c8a1d5b0190b214360dc032",
      name: "Devcentral Bootcamp",
      description:
        "Is coding your passion? Codemasters will give you the skills and the tools to become the best developer possible. We specialize in front end and full stack web development",
      website: "https://devcentral.com",
      phone: "(444) 444-4444",
      email: "enroll@devcentral.com",
      createdAt: "2019-11-20T10:05:07.447Z",
      slug: "devcentral-bootcamp",
      __v: 0,
      averageCost: 6340,
      courses: [
        {
          scholarshipAvailable: false,
          _id: "5d725cfec4ded7bcb480eaa7",
          title: "IOS Development",
          description:
            "Get started building mobile applications for IOS using Swift and other tools",
          weeks: "8",
          tuition: 6000,
          minimumSkill: "intermediate",
          bootcamp: "5d725a1b7b292f5f8ceff788",
          user: "5c8a1d5b0190b214360dc032",
          createdAt: "2019-11-20T10:05:11.655Z",
          __v: 0
        },
        {
          scholarshipAvailable: false,
          _id: "5d725cfec4ded7bcb480eaa6",
          title: "Software QA",
          description:
            "This course will teach you everything you need to know about quality assurance",
          weeks: "6",
          tuition: 5000,
          minimumSkill: "intermediate",
          bootcamp: "5d725a1b7b292f5f8ceff788",
          user: "5c8a1d5b0190b214360dc032",
          createdAt: "2019-11-20T10:05:11.654Z",
          __v: 0
        },
        {
          scholarshipAvailable: false,
          _id: "5d725cfec4ded7bcb480eaa5",
          title: "Web Development",
          description:
            "This course will teach you how to build high quality web applications with technologies like React, Node.js, PHP & Laravel",
          weeks: "8",
          tuition: 8000,
          minimumSkill: "beginner",
          bootcamp: "5d725a1b7b292f5f8ceff788",
          user: "5c8a1d5b0190b214360dc032",
          createdAt: "2019-11-20T10:05:11.653Z",
          __v: 0
        }
      ],
      id: "5d725a1b7b292f5f8ceff788"
    },
    {
      location: {
        type: "Point",
        coordinates: [-73.200576, 44.478305],
        formattedAddress: "85 S Prospect St, Burlington, VT 05401-3444, US",
        street: "85 S Prospect St",
        city: "Burlington",
        state: "VT",
        zipcode: "05401-3444",
        country: "US"
      },
      careers: ["Web Development", "Data Science", "Business"],
      photo: "no-photo.jpg",
      housing: false,
      jobAssistance: false,
      jobGuarantee: false,
      acceptGi: false,
      _id: "5d725a037b292f5f8ceff787",
      user: "5c8a1d5b0190b214360dc031",
      name: "Codemasters",
      description:
        "Is coding your passion? Codemasters will give you the skills and the tools to become the best developer possible. We specialize in full stack web development and data science",
      website: "https://codemasters.com",
      phone: "(333) 333-3333",
      email: "enroll@codemasters.com",
      createdAt: "2019-11-20T10:05:07.446Z",
      slug: "codemasters",
      __v: 0,
      averageCost: 10500,
      courses: [
        {
          scholarshipAvailable: false,
          _id: "5d725cfec4ded7bcb480eaa4",
          title: "Data Science Program",
          description:
            "In this course you will learn Python for data science, machine learning and big data tools",
          weeks: "10",
          tuition: 9000,
          minimumSkill: "intermediate",
          bootcamp: "5d725a037b292f5f8ceff787",
          user: "5c8a1d5b0190b214360dc031",
          createdAt: "2019-11-20T10:05:11.651Z",
          __v: 0
        },
        {
          scholarshipAvailable: false,
          _id: "5d725ce8c4ded7bcb480eaa3",
          title: "Web Design & Development",
          description:
            "Get started building websites and web apps with HTML/CSS/JavaScript/PHP. We teach you",
          weeks: "10",
          tuition: 12000,
          minimumSkill: "beginner",
          bootcamp: "5d725a037b292f5f8ceff787",
          user: "5c8a1d5b0190b214360dc031",
          createdAt: "2019-11-20T10:05:11.651Z",
          __v: 0
        }
      ],
      id: "5d725a037b292f5f8ceff787"
    },
    {
      location: {
        type: "Point",
        coordinates: [-71.324239, 42.650484],
        formattedAddress: "220 Pawtucket St, Lowell, MA 01854-3502, US",
        street: "220 Pawtucket St",
        city: "Lowell",
        state: "MA",
        zipcode: "01854-3502",
        country: "US"
      },
      careers: ["Web Development", "UI/UX", "Mobile Development"],
      photo: "no-photo.jpg",
      housing: false,
      jobAssistance: true,
      jobGuarantee: false,
      acceptGi: true,
      _id: "5d713a66ec8f2b88b8f830b8",
      user: "5d7a514b5d2c12c7449be046",
      name: "ModernTech Bootcamp",
      description:
        "ModernTech has one goal, and that is to make you a rockstar developer and/or designer with a six figure salary. We teach both development and UI/UX",
      website: "https://moderntech.com",
      phone: "(222) 222-2222",
      email: "enroll@moderntech.com",
      createdAt: "2019-11-20T10:05:07.444Z",
      slug: "moderntech-bootcamp",
      __v: 0,
      averageCost: 11000,
      courses: [
        {
          scholarshipAvailable: false,
          _id: "5d725cb9c4ded7bcb480eaa1",
          title: "Full Stack Web Dev",
          description:
            "In this course you will learn all about the front end with HTML, CSS and JavaScript. You will master tools like Git and Webpack and also learn C# and ASP.NET with Postgres",
          weeks: "10",
          tuition: 12000,
          minimumSkill: "intermediate",
          bootcamp: "5d713a66ec8f2b88b8f830b8",
          user: "5d7a514b5d2c12c7449be046",
          createdAt: "2019-11-20T10:05:11.649Z",
          __v: 0
        },
        {
          scholarshipAvailable: false,
          _id: "5d725cd2c4ded7bcb480eaa2",
          title: "UI/UX",
          description:
            "In this course you will learn to create beautiful interfaces. It is a mix of design and development to create modern user experiences on both web and mobile",
          weeks: "12",
          tuition: 10000,
          minimumSkill: "intermediate",
          bootcamp: "5d713a66ec8f2b88b8f830b8",
          user: "5d7a514b5d2c12c7449be046",
          createdAt: "2019-11-20T10:05:11.650Z",
          __v: 0
        }
      ],
      id: "5d713a66ec8f2b88b8f830b8"
    },
    {
      location: {
        type: "Point",
        coordinates: [-71.104028, 42.350846],
        formattedAddress: "233 Bay State Rd, Boston, MA 02215-1405, US",
        street: "233 Bay State Rd",
        city: "Boston",
        state: "MA",
        zipcode: "02215-1405",
        country: "US"
      },
      careers: ["Web Development", "UI/UX", "Business"],
      photo: "no-photo.jpg",
      housing: true,
      jobAssistance: true,
      jobGuarantee: false,
      acceptGi: true,
      _id: "5d713995b721c3bb38c1f5d0",
      user: "5d7a514b5d2c12c7449be045",
      name: "Devworks Bootcamp",
      description:
        "Devworks is a full stack JavaScript Bootcamp located in the heart of Boston that focuses on the technologies you need to get a high paying job as a web developer",
      website: "https://devworks.com",
      phone: "(111) 111-1111",
      email: "enroll@devworks.com",
      createdAt: "2019-11-20T10:05:07.438Z",
      slug: "devworks-bootcamp",
      __v: 0,
      averageCost: 9000,
      averageRating: 9,
      courses: [
        {
          scholarshipAvailable: false,
          _id: "5d725c84c4ded7bcb480eaa0",
          title: "Full Stack Web Development",
          description:
            "In this course you will learn full stack web development, first learning all about the frontend with HTML/CSS/JS/Vue and then the backend with Node.js/Express/MongoDB",
          weeks: "12",
          tuition: 10000,
          minimumSkill: "intermediate",
          bootcamp: "5d713995b721c3bb38c1f5d0",
          user: "5d7a514b5d2c12c7449be045",
          createdAt: "2019-11-20T10:05:11.648Z",
          __v: 0
        },
        {
          scholarshipAvailable: false,
          _id: "5d725a4a7b292f5f8ceff789",
          title: "Front End Web Development",
          description:
            "This course will provide you with all of the essentials to become a successful frontend web developer. You will learn to master HTML, CSS and front end JavaScript, along with tools like Git, VSCode and front end frameworks like Vue",
          weeks: "8",
          tuition: 8000,
          minimumSkill: "beginner",
          bootcamp: "5d713995b721c3bb38c1f5d0",
          user: "5d7a514b5d2c12c7449be045",
          createdAt: "2019-11-20T10:05:11.647Z",
          __v: 0
        }
      ],
      id: "5d713995b721c3bb38c1f5d0"
    }
  ]
};

Finally, here is a CodeSandbox demo.

Answer 1

You're setting an Object to the state , set the data array instead :

useEffect(() => {
    setState(api.data);
    //console.log(state)
  }, [state]);

and return something from mapping() :

const maping = () => {
    return state.map((item, index) => ( ...
  }

Answer 2

As @Taki mentioned, you have to set the array data to your state, and you cannot render object as your children in react. Assuming that you want to render all the list's name, you have to write item.name in your maping function, also remember to return your map function.

I've removed the state from your useEffect deps array.

useEffect(() => {
  setState(api.data);
}, []);

const maping = () => {
  return state.map((item, index) => <h3 key={index}>{item.name}</h3>);
};

Answer 3

The only thing you are lacking is the return statement.

In addition, you should not return the entire item object, as you should be returning a string or number value to be displayed on the DOM. You might want to use the id rather than the index for the key attribute.

const maping = () => {
  return state.map((item, index) => <h3 key={item._id}>{item.name}</h3>);
};

Another thing to take note is that, you should not nest your <h3> tags within an empty <h2> tag, as it is not an appropriate HTML statement. You might nest in within a <div> tag, or react fragment , as denoted by the shorthand syntax <></> .

return (
  <div className="App">
    <h3> json data rendering test</h3>
    <>{maping()}</>
  </div>
);