我试图 map 数据库中的数据并收到此错误。 TypeError：无法读取未定义的属性“地图”

Question

I am trying to map the data from the database and getting this error. TypeError: Cannot read property 'map' of undefined

 import React from "react";
    
    export default class Allusers extends React.Component {
      state = {
        people: [],
      };
    
      async componentDidMount() {
        const url = "http://localhost:5000/dashboard/getuser";
        const response = await fetch(url);
        const data = await response.json();
        console.log(data);
        this.setState({ people: data.results });
      }
    
      render() {
        //const peopleJSX = [];
    
        //this.state.people.forEach((person) => {
        //peopleJSX.push(
        //<div key={person.id}>
        //<div>{person.firstname}</div>
        //<div>{person.lasttname}</div>
        //</div>
        //);
        //});
    
        return (
          <div>
            {this.state.people.map((person) => (
              <div key={person.id}>
                <div>{person.firstname}</div>
                <div>{person.lasttname}</div>
              </div>
            ))}
          </div>
        );
      }
    }

FYI my API is working I have tested it on Postman.

This is the screenshot of my error

Answer 1

You need to put the state inside of the constructor of the class like the example below:

class Clock extends React.Component {
  constructor(props) {
    super(props);
    this.state = {date: new Date()};
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>It is {this.state.date.toLocaleTimeString()}.</h2>
      </div>
    );
  }
}

The code is from this example: https://reactjs.org/docs/state-and-lifecycle.html . Right now you just have a variable named state and it's not bound to the class.

Answer 2

There is the correction in the above code. Instead of:

this.setState({ people: data.results });

Use:

this.setState({ people: data.gigs });

as the gigs are the key of the object in which the data is stored.