eslint：缺少迭代器中元素的“key”道具（react/jsx-key）

Question

I am new to React, and I'm trying to output a table containing the information of users. But Eslint is keep giving me the following error:

[eslint] Missing "key" prop for element in iterator [react/jsx-key]

I am not sure if I did this properly, but I have assigned a unique ID number for each person in the user list, but not sure why the error is persistent.

So in my PeopleCard.js I have the following:

import React from "react";
import {
  Card,
  CardImg,
  CardText,
  CardBody,
  CardTitle,
  CardSubtitle,
  Button
} from "reactstrap";
import PropTypes from "prop-types";

class PeopleCard extends React.Component {
  static propTypes = {
    person: PropTypes.object,
    id: PropTypes.number,
    name: PropTypes.string,
    company: PropTypes.string,
    description: PropTypes.string
  };
  render() {
    return (
      <div>
        <Card>
          <CardImg
            top
            width="100%"
            src="https://via.placeholder.com/318x180.png"
            alt="Card image cap"
          />
          <CardBody>
            <CardTitle>{this.props.person.name}</CardTitle>
            <CardSubtitle>{this.props.person.company}</CardSubtitle>
            <CardText>{this.props.person.description}</CardText>
            <Button>Button</Button>
          </CardBody>
        </Card>
      </div>
    );
  }
}

export default PeopleCard;

And in my MainArea.js, I have the following:

import React from "react";
import { Container, Row, Col } from "reactstrap";
import PeopleCard from "./PeopleCard";

class MainArea extends React.Component {
  constructor() {
    super();
    this.state = {
      people: [
        {
          id: 1,
          name: "John",
          company: "Some Company, Inc",
          description: "Met at a party."
        },
        {
          id: 2,
          name: "Mary",
          company: "Some Company, Inc",
          description: "Met at a party."
        },
        {
          id: 3,
          name: "Jane",
          company: "Some Company, Inc",
          description: "Met at a party."
        }
      ]
    };
  }
  render() {
    let peopleCard = this.state.people.map(person => {
      return (
        <Col sm="4">
          <PeopleCard key={person.id} person={person} />
        </Col>
      );
    });
    return (
      <Container fluid>
        <Row>{peopleCard}</Row>
      </Container>
    );
  }
}

export default MainArea;

The following line is throwing the error, and I cannot figure out why:

<Col sm="4">
   <PeopleCard key={person.id} person={person} />
</Col>

How can I prevent this error from appearing?

Answer 1

You should put the key on the outer element:

const peopleCard = this.state.people.map(person => (
  <Col key={person.id} sm="4">
    <PeopleCard person={person} />
  </Col>
));

Answer 2

sometime it still give issue if your two key values get match so better use this way.

 render() {
let peopleCard = this.state.people.map((person, index) => {
  return (
    <Col sm="4" key={`${person.id}+${index}`}>
      <PeopleCard key={person.id} person={person} />
    </Col>
  );
});
return (
  <Container fluid>
    <Row>{peopleCard}</Row>
  </Container>
);

}

were no two loop will have same id with index which can make key value different.